Liquefied gas-fuel supply device for diesel engine

ABSTRACT

Since an aspirator  7  is disposed at a position lower than a fuel gallery  11  and an overflow fuel pipe  81 , DME fuel remaining in the fuel gallery  11  and the overflow fuel pipe  81  can be more efficiently retrieved to a fuel tank  4  by a combined force of gravity and suction force produced in a suction port  7   c  of the aspirator  7 . Since the vapor-phase pressure delivery pipe opening/closing solenoid valve  74  is disposed at a position higher than the fuel gallery  11 , DME fuel in a liquid state remaining in the fuel gallery  11  and the overflow fuel pipe  81  is forcedly delivered under pressure to the suction port  7   c  of the aspirator  7  by a combined force of gravity and the pressure of a vapor phase  4   b  in the fuel tank  4 . Accordingly, time taken to retrieve the DME fuel in an injection system to the fuel tank after the stop of a diesel engine.

TECHNICAL FIELD

The present invention relates to a liquefied gas fuel supply device fora diesel engine which uses, as fuel, liquefied gas such as DME (dimethylether) or LP gas to which a cetane number improver is added (hereinafterreferred to as “high cetane number LP gas”).

BACKGROUND ART

A diesel engine which uses clean-burning fuels such as DME (dimethylether) and high cetane number LP gas instead of light oil is nowattracting attention as air pollution abatement measures for dieselengines. These fuels are liquefied gas fuels unlike light oil which is aconventional fuel. Namely, liquefied gas fuels have boiling points lowerthan that of light oil, and have the nature of vaporizing at roomtemperature, whereas light oil exists as a liquid under atmosphericpressure at room temperature. For this reason, in the case of a dieselengine using liquefied gas fuel, after the stop of the diesel engine,liquefied gas fuel remaining in an injection system which is a fuelsupply line section leading to a fuel injection nozzle leaks from anozzle seat part of the fuel injection nozzle into a cylinder of thediesel engine and vaporizes in the cylinder. As a result, vaporized DMEfuel is charged in the cylinder, and when the diesel engine is to bestarted at the next time, there is a risk that abnormal combustion suchas knocking occurs and the diesel engine cannot be normally started andlarge vibrations and noise occur.

As one example of related arts for solving this problem, there is, forexample, an injection system (for example, Japanese Patent No. 3111254)which includes at least one heating device and means for formingconnection which permits a flow between at least one pressure guidesection of an injection system and a fuel tank, after the stop of a fuelsupply device (such as an injection pump). The injection system formsconnection between at least one pressure guide section of the injectionsystem and the fuel tank after the stop of the fuel supply device, heatsat least a part of the pressure guide section to transfer remainingliquefied gas fuel such as DME to a vapor phase and produce a gas blow,and press the remaining liquefied gas fuel of the pressure guide sectionto the fuel tank by the gas blow. In addition, there is a diesel enginefuel system (for example, JP-A-11-107871) which detects three pressureparameters, atmospheric pressure, fuel tank internal pressure and fuelreturn pipe internal pressure, and retrieves remaining liquefied gasfuel to a fuel tank by using the difference between these pressures.

In each of the above-mentioned related arts, as means for retrieving theliquefied gas fuel remaining in the pressure guide section such as afuel return pipe to the fuel tank after the stop of the fuel supplydevice, it is necessary to incorporate not only means for switching pipepassages by solenoid valves or the like, but also at least one heatingdevice (Japanese Patent No. 3111254) or a pressure sensor for detectingthe fuel return pipe internal pressure (JP-A-11-107871). Accordingly, ina fuel supply system for a diesel engine, there is a risk that means forretrieving remaining fuel after the stop of the fuel supply devicebecomes expensive and the main cause of increasing the cost of the fuelsupply system.

The present applicant has previously proposed a liquefied gas fuelsupply device including means for retrieving remaining liquefied gasfuel to a fuel tank by aspiration means using an aspirator, as means forretrieving liquefied gas fuel remaining in an injection system to thefuel tank after the stop of the fuel supply device (Application Number2002-60829). This means for retrieving remaining fuel through theaspirator forms a ring-shaped flow of liquefied gas fuel including theaspirator by using as a driving source a feed pump for deliveringliquefied gas fuel from the fuel tank in its original use, and sucks theliquefied gas fuel remaining in the injection system by suction forceproduced in the aspirator by the flow of the liquefied gas fuel, therebyretrieving the remaining liquefied gas fuel to the fuel tank. Namely,the liquefied gas fuel remaining in the injection system can beretrieved only by the means for forming the ring-shaped flow passage ofliquefied gas fuel by the aspirator and the feed pump, whereby theliquefied gas fuel remaining in the injection system after the stop ofthe fuel supply device without the need to provide a heating device, apressure sensor or the like. Accordingly, it is possible to constructthe remaining-fuel retrieving means at low cost.

However, the present inventor has promoted further intensive researchand discovered that if the liquefied gas fuel remaining in the injectionsystem of the liquefied gas fuel supply device after the stop of thediesel engine is to be sucked into the fuel tank by the suction meansusing the aspirator, a comparatively long time is required to suck allthe liquefied gas fuel remaining in the injection system. This isbecause the suction force by the aspirator having no driving source isweak compared to pumps or the like having driving sources. As a result,a certain extent of time is required to retrieve all the liquefied gasfuel remaining in the injection system of the liquefied gas fuel supplydevice, and if the diesel engine is again started after the dieselengine is stopped for a short time, the diesel engine is restarted inspite of the fact that all the liquefied gas fuel remaining in theinjection system of the liquefied gas fuel supply device is not yetretrieved, so that there is a risk that abnormal combustion such asknocking occurs.

In addition, when the diesel engine is again started after the dieselengine has been stopped, liquefied gas fuel needs to be charged into theinjection system of the liquefied gas fuel supply device before thediesel engine is started. Therefore, the diesel engine cannot be startedwhile liquefied gas fuel is being charged into the injection system ofthe liquefied gas fuel supply device. In addition, since a long time isrequired to charge liquefied gas fuel into the injection system of theliquefied gas fuel supply device, there is the problem that the dieselengine cannot be rapidly started when the diesel engine and theliquefied gas fuel supply device are stopped.

DISCLOSURE OF THE INVENTION

The invention has been made in view of the above-mentioned problems, andan object of the invention is to reduce time taken to retrieve liquefiedgas fuel in an injection system to a fuel tank after the stop of adiesel engine in a liquefied gas fuel supply device for a diesel engine.

Another object of the invention is to reduce time taken to chargeliquefied gas fuel into an injection system from a fuel tank at thestarting time of a diesel engine in a liquefied gas fuel supply devicefor a diesel engine.

To achieve the above objects, a first aspect of the invention provides aliquefied gas fuel supply device for a diesel engine characterized bycomprising: a fuel tank for reserving liquefied gas fuel; an injectionpump for delivering liquefied gas fuel to a fuel injection nozzle of adiesel engine; fuel supply means for delivering the liquefied gas fuelfrom the fuel tank to the injection pump; and remaining fuel retrievingmeans for retrieving liquefied gas fuel remaining in the injection pumpto the fuel tank, after the stop of the diesel engine. The remainingfuel retrieving means is constructed to cause forced circulation of theliquefied gas fuel in the fuel tank back so as to again return theliquefied gas fuel to the fuel tank through an aspirator, and retrievethe liquefied gas fuel remaining in the injection pump to the fuel tankby suction force produced in a suction port of the aspirator by theforced circulation, and the suction port of the aspirator is disposed ata position lower than an area in the injection pump in which theliquefied gas fuel remains.

According to the invention, the suction port of the aspirator isdisposed at a position lower than the area in the injection pump inwhich the liquefied gas fuel remains. Namely, an area in each of thefuel gallery and the overflow fuel pipe in which the liquefied gas fuelremains after the stop of the liquefied gas fuel supply device isdisposed at a position higher than the suction port of the aspirator.Accordingly, the liquefied gas fuel remaining in the area is retrievedto the fuel tank by a combined force of gravity and the suction forceproduced by the circulation of the liquefied gas fuel, whereby it ispossible to more efficiently retrieve liquefied gas fuel remaining in aninjection system, by using gravity. Accordingly, it is possible toachieve the effect and advantage of reducing time taken to retrieve theliquefied gas fuel in the injection system to the fuel tank after thestop of the diesel engine.

A second aspect of the invention provides a liquefied gas fuel supplydevice for a diesel engine characterized by comprising: a feed pump forpressurizing liquefied gas fuel in a fuel tank to a predeterminedpressure and delivering the liquefied gas fuel to a feed pipe; aninjection pump for delivering the liquefied gas fuel in a fuel galleryinto which the liquefied gas fuel delivered via the feed pipe flows, toan injection nozzle of a diesel engine by a predetermined amount atpredetermined timing; an overflow fuel pipe for returning to the fueltank the liquefied gas fuel which overflows from the injection pump; andremaining fuel retrieving means for retrieving to the fuel tank theliquefied gas fuel remaining in the fuel gallery and the overflow fuelpipe, after the stop of the diesel engine. The remaining fuel retrievingmeans has: a fuel circulation pipe branched from the feed pipe at anintermediate point thereof and connected to the fuel tank; feed pipeopening/closing means provided in the feed pipe on a side downstream ofthe feed pump in a flowing direction of the liquefied gas fuel, andoperative to open and close a flow passage of the feed pipe; and anaspirator provided in the fuel circulation pipe and having a suctionport disposed to communicate with the fuel gallery and/or the overflowfuel pipe. The remaining fuel retrieving means is constructed tocirculate the liquefied gas fuel delivered from the feed pump, to thefuel tank via the feed pipe, the fuel circulation pipe and the aspiratorin the state of cutting off supply to the injection pump by closing thefeed pipe opening/closing means, and suck and retrieve the liquefied gasfuel remaining in the fuel gallery and the overflow fuel pipe, to thefuel tank by suction force produced in the suction port of the aspiratoron the basis of the circulation. The suction port of the aspirator isdisposed at a position lower than the fuel gallery and the overflow fuelpipe.

In this manner, the suction port of the aspirator in which the suctionforce is produced by the circulation of the liquefied gas fuel isdisposed at a position lower than the fuel gallery and the overflow fuelpipe. Namely, the fuel gallery and the overflow fuel pipe in which theliquefied gas fuel remains after the stop of the liquefied gas fuelsupply device are disposed at a position higher than the suction port ofthe aspirator. Accordingly, the liquefied gas fuel remaining in the fuelgallery and the overflow fuel pipe is retrieved to the fuel tank by acombined force of gravity and the suction force produced by thecirculation of the liquefied gas fuel, whereby it is possible to moreefficiently retrieve the liquefied gas fuel remaining in the injectionsystem, by using gravity. Accordingly, it is possible to achieve theeffect and advantage of reducing time taken to retrieve the DME fuel inthe injection system to the fuel tank after the stop of the dieselengine.

A third aspect of the invention is characterized by further comprisingin the second aspect a check valve disposed between a position where thefuel circulation pipe is branched from the feed pipe and the feed pipeopening/closing means, and operative to prevent liquefied gas fuel fromflowing back from the injection pump, and fuel circulation pipeopening/closing means provided in the fuel circulation pipe andoperative to open and close a flow passage of the fuel circulation pipe.

A fourth aspect of the invention provides a liquefied gas fuel supplydevice for a diesel engine characterized by comprising: a feed pump forpressurizing liquefied gas fuel in a fuel tank to a predeterminedpressure and delivering the liquefied gas fuel to a feed pipe; aninjection pump for delivering the liquefied gas fuel in a fuel galleryinto which the liquefied gas fuel delivered via the feed pipe flows, toan injection nozzle of a diesel engine by a predetermined amount atpredetermined timing; an overflow fuel pipe for returning to the fueltank the liquefied gas fuel which overflows from the injection pump; andremaining fuel retrieving means for retrieving to the fuel tank theliquefied gas fuel remaining in the fuel gallery and the overflow fuelpipe, after the stop of the diesel engine. The remaining fuel retrievingmeans has: a fuel circulation pipe branched from the feed pipe at anintermediate point thereof and connected to the fuel tank; feed pipeopening/closing means provided in the feed pipe on a side downstream ofthe feed pump in a flowing direction of the liquefied gas fuel, andoperative to open and close a flow passage of the feed pipe; and anaspirator provided in the fuel circulation pipe and having a suctionport disposed to communicate with the fuel gallery and/or the overflowfuel pipe. The remaining fuel retrieving means is constructed tocirculate the liquefied gas fuel delivered from the feed pump, to thefuel tank via the feed pipe, the fuel circulation pipe and the aspiratorin the state of cutting off supply to the injection pump by closing thefeed pipe opening/closing means, and suck and retrieve the liquefied gasfuel remaining in the fuel gallery and the overflow fuel pipe, to thefuel tank by suction force produced in the suction port of the aspiratoron the basis of the circulation. The remaining fuel retrieving meansfurther includes: fuel circulation pipe opening/closing means providedin the fuel circulation pipe and operative to open and close a flowpassage of the fuel circulation pipe; and a check valve disposed betweena branch point between the feed pipe and the fuel circulation pipe andthe feed pipe opening/closing means, and operative to prevent liquefiedgas fuel from flowing back from the injection pump.

The fuel circulation pipe is branched from the feed pipe in the vicinityof a delivery port of the feed pump, and is connected to the fuel tankvia the inlet and the outlet of the aspirator. When the feed pipeopening/closing means is closed to cut off the communication of the feedpipe on the same side as the injection pump with respect to the branchpoint between the feed pipe and the fuel circulation pipe and the fuelcirculation pipe opening/closing means is opened and the feed pump isactivated with the fuel circulation pipe permitted to communicate, aring-shaped flow of liquefied gas fuel including the aspirator isformed, and the suction force is produced in the suction port of theaspirator. During this state, when the suction port of the aspirator,the fuel gallery and the overflow fuel pipe are communicated with oneanother, the liquefied gas fuel remaining in the fuel gallery and theoverflow fuel pipe can be sucked from the suction port of the aspirator.The liquefied gas fuel sucked from the suction port of the aspirator isretrieved to the fuel tank together with the liquefied gas fuel flowingfrom the inlet to the outlet of the aspirator.

In addition, since the fuel circulation pipe which constitutes acirculation passage is branched from the feed pipe in the vicinity ofthe delivery port of the feed pump and is connected to the fuel tankfrom the inlet to the outlet of the aspirator, the circulation passageof the liquefied gas fuel can be compactly constructed. Namely, sincethe length of the circulation passage of liquefied gas fuel includingthe aspirator can be made short, and the flow passage resistance of thecirculation passage can be made small. Accordingly, a decrease due tothe flow passage resistance in the flow rate of liquefied gas fuelflowing in the circulation passage can be reduced, and a decrease in thesuction force produced in the suction port of the aspirator can bereduced, whereby it is possible to improve the efficiency of retrievingof remaining fuel by the aspirator.

In addition, since a check valve for preventing liquefied gas fuel fromflowing back from the injection pump is disposed between the branchpoint where the fuel circulation pipe is branched from the feed pipe andthe feed pipe opening/closing means, the feed pipe between the sameremains charged with liquefied gas fuel. The liquefied gas fuel chargedbetween the feed pipe opening/closing means and the check valve does notflow into the injection pump, as long as the feed pipe opening/closingmeans on the side of the injection pump is closed. Accordingly, theabove-mentioned abnormal combustion such as knocking is prevented fromoccurring, owing to the liquefied gas fuel charged between the feed pipeopening/closing means and the check valve, whereby it is not necessaryto retrieve the liquefied gas fuel remaining charged between the feedpipe opening/closing means and check vale by the remaining fuelretrieving means.

Then, after the liquefied gas fuel remaining in the fuel gallery and theoverflow fuel pipe has been retrieved by means of the aspirator byappropriately opening and closing the fuel circulation pipeopening/closing means and the feed pipe opening/closing means, the fuelcirculation pipe opening/closing means is closed with the feed pipeopening/closing means remaining closed, and the feed pipe is stopped andthe liquefied gas fuel supply device is stopped. Accordingly, theliquefied gas fuel can be held in the state of being charged between thefeed pipe opening/closing means and the check valve. Accordingly, it ispossible to reduce the amount of liquefied gas fuel to be retrieved bythe remaining fuel retrieving means after the stop of the diesel engine.Furthermore, after the stop of the diesel engine, the liquefied gas fuelis held in the state of being charged between the feed pipeopening/closing means of the feed pipe and the check valve, whereby itis possible to reduce the amount of liquefied gas fuel to be chargedinto the injection system at the next time when the diesel engine is tobe started.

According to the liquefied gas fuel supply device for a diesel engineaccording to the fourth aspect of the invention, it is possible toimprove the efficiency of retrieving of remaining fuel by the aspirator,and it is also possible to reduce the amount of liquefied gas fuel to beretrieved by the remaining fuel retrieving means after the stop of thediesel engine. Accordingly, it is possible to achieve the effect andadvantage of reducing time taken to retrieve the liquefied gas fuel inthe injection system to the fuel tank after the stop of the dieselengine.

In addition, since it is possible to reduce the amount of liquefied gasfuel to be charged into the injection system at the starting time of thediesel engine, it is possible to achieve the effect and advantage ofreducing time taken to charge liquefied gas fuel into the injectionsystem from the fuel tank at the starting time of the diesel engine.

In addition, the suction port of the aspirator in which the suctionforce is produced by the circulation of liquefied gas fuel is disposedat a position lower than an area in the fuel gallery, the overflow fuelpipe liquefied gas fuel or the like in which area the liquefied gas fuelremains. Namely, each of the fuel gallery and the overflow fuel pipe inwhich the liquefied gas fuel remains after the stop of the liquefied gasfuel supply device is disposed at a position higher than the suctionport of the aspirator. Accordingly, the liquefied gas fuel remaining inthe fuel gallery and the overflow fuel pipe is retrieved to the fueltank by a combined force of gravity and the suction force produced bythe circulation of the liquefied gas fuel, whereby it is possible tomore efficiently retrieve the liquefied gas fuel remaining in theinjection system, by using gravity. Accordingly, it is possible toachieve the effect and advantage of reducing time taken to retrieve theliquefied gas fuel in the injection system to the fuel tank after thestop of the diesel engine.

A fifth aspect of the invention provides a liquefied gas fuel supplydevice for a diesel engine according to any one of the first to fourthaspects is characterized by further comprising a vapor-phase pressuredelivery pipe connecting an inlet for liquefied gas fuel in theinjection pump and a vapor phase in the fuel tank, and vapor-phasepressure delivery pipe opening/closing means for opening and closing thevapor-phase pressure delivery pipe.

The vapor phase in the fuel tank and the inlet of the fuel gallery arecommunicated with each other by the vapor-phase pressure delivery pipeby opening the vapor-phase pressure delivery pipe opening/closing meansafter the stop of the diesel engine, whereby the pressure of the vaporphase in the fuel tank acts on the fuel gallery. In the vapor phase inthe fuel tank, vaporized liquefied gas fuel exists under higher pressurethan the pressure in the fuel gallery, whereby the liquefied gas fuel ina liquid state remaining in the fuel gallery and the overflow fuel pipecan be forcedly delivered under pressure to the remaining fuelretrieving means by the pressure of the vapor phase in the fuel tank.Accordingly, it is possible to achieve the effect and advantage ofreducing time taken to retrieve the liquefied gas fuel remaining in thefuel gallery and the overflow fuel pipe by the remaining fuel retrievingmeans.

A sixth aspect of the invention provides a liquefied gas fuel supplydevice for a diesel engine according to the fifth aspect, characterizedin that the vapor-phase pressure delivery pipe opening/closing means isdisposed at a position higher than an area in the injection pump inwhich the liquefied gas fuel remains.

In this manner, since the vapor-phase pressure delivery pipeopening/closing means is disposed at a position higher than the fuelgallery, the liquefied gas fuel in a liquid state remaining in the fuelgallery and the overflow fuel pipe is forcedly delivered under pressureto the remaining fuel retrieving means by a combined force of gravityand the pressure of the vapor phase in the fuel tank. Accordingly,gravity can be used to more efficiently deliver under pressure theliquefied gas fuel in a liquid state remaining in the fuel gallery andthe overflow fuel pipe to the remaining fuel retrieving means, wherebyit is possible to further reduce time taken to retrieve the liquefiedgas fuel remaining in the fuel gallery and the overflow fuel pipe to thefuel tank by the remaining fuel retrieving means.

A seventh aspect of the invention provides a liquefied gas fuel supplydevice for a diesel engine according to any one of the first to fourthaspects, characterized by including a construction in which theliquefied gas fuel delivered from the injection pump is supplied to acommon rail and is delivered to each fuel injection nozzle from thecommon rail, and further comprising a vapor-phase pressure delivery pipeconnecting the common rail and a vapor phase in the fuel tank, andvapor-phase pressure delivery pipe opening/closing means for opening andclosing the vapor-phase pressure delivery pipe.

In a common rail diesel engine, the liquefied gas fuel remaining in thecommon rail also needs to be retrieved to the fuel tank when the dieselengine is to be stopped. In this manner, the vapor phase in the fueltank and the common rail are disposed to communicate with each other bythe vapor-phase pressure delivery pipe, and when the vapor-phasepressure delivery pipe opening/closing means is opened after the stop ofthe diesel engine, the vapor phase in the fuel tank and the common railcommunicate with each other through the vapor-phase pressure deliverypipe, whereby the pressure of the vapor phase in the fuel tank acts onthe inside of the common rail. In the vapor phase in the fuel tank,vaporized liquefied gas fuel exists under higher pressure than thepressure in the fuel gallery, whereby the liquefied gas fuel in a liquidstate remaining in the common rail can be forcedly delivered underpressure to the remaining fuel retrieving means by the pressure of thevapor phase in the fuel tank. Accordingly, it is possible to achieve theeffect and advantage of further reducing time taken to retrieve theliquefied gas fuel remaining in the common rail to the fuel tank by theremaining fuel retrieving means.

An eighth aspect of the invention provides a liquefied gas fuel supplydevice for a diesel engine according to the seventh aspect,characterized in that the vapor-phase delivery pipe opening/closingmeans is disposed at a position higher than the common rail.

In this manner, the vapor-phase pressure delivery pipe opening/closingmeans is disposed at a position higher than the common rail, theliquefied gas fuel in a liquid state remaining in the common rail isforcedly delivered under pressure to the remaining fuel retrieving meansby a combined force of gravity and the pressure of the vapor phase inthe fuel tank. Accordingly, since the liquefied gas fuel in a liquidstate remaining in the common rail can be more efficiently deliveredunder pressure to the remaining fuel retrieving means by using gravity,it is possible to achieve the effect and advantage of further reducingtime taken to retrieve the liquefied gas fuel remaining in the commonrail to the fuel tank by the remaining fuel retrieving means.

A ninth aspect of the invention provides a liquefied gas fuel supplydevice for a diesel engine according to any one of the first and fourthaspects, characterized by including a construction in which theliquefied gas fuel delivered from the injection pump is supplied to acommon rail and is delivered to each fuel injection nozzle from thecommon rail, and further comprising a vapor-phase pressure delivery pipeconnecting an inlet of the fuel injection nozzle and a vapor phase inthe fuel tank, and vapor-phase pressure delivery pipe opening/closingmeans for opening and closing the vapor-phase pressure delivery pipe.

In this manner, each fuel injection nozzle and the vapor phase in thefuel tank are disposed to communicate with each other by the vapor-phasepressure delivery pipe, and when the vapor-phase pressure delivery pipeopening/closing means is opened after the stop of the diesel engine, thevapor phase in the fuel tank and each fuel injection nozzle communicatewith each other through the vapor-phase pressure delivery pipe, wherebythe pressure of the vapor phase in the fuel tank acts on the inside ofeach fuel injection nozzle. In the vapor phase in the fuel tank,vaporized liquefied gas fuel exists under higher pressure than thepressure in the fuel gallery, whereby the liquefied gas fuel in a liquidstate remaining in each fuel injection nozzle can be forcedly deliveredunder pressure to the remaining fuel retrieving means by the pressure ofthe vapor phase in the fuel tank. In a general common rail type of fuelsupply device, a fuel injection nozzle is disposed at the highestposition, a common rail and an injection pump at the second highestposition, and a fuel tank at the lowest position. Namely, the liquefiedgas fuel remaining in each of the fuel injection nozzle, the common railand the injection pump (the fuel gallery) can be forcedly deliveredunder pressure to the remaining fuel retrieving means in order from thehighest position by vapor-phase pressure and gravity. Accordingly, it ispossible to achieve the effect and advantage of further reducing timetaken to retrieve the liquefied gas fuel remaining in the fuel injectionnozzle to the fuel tank by the remaining fuel retrieving means.

A tenth aspect of the invention provides a liquefied gas fuel supplydevice for a diesel engine according to the ninth aspect, characterizedin that the vapor-phase pressure delivery pipe opening/closing means isdisposed at a position higher than the fuel injection nozzle.

Since the vapor-phase pressure delivery pipe opening/closing means isdisposed at a position higher than each fuel injection nozzle in thismanner, the liquefied gas fuel remaining in each fuel injection nozzleis forcedly delivered under pressure to the remaining fuel retrievingmeans by a combined force of gravity and the pressure of the vapor phasein the fuel tank. Accordingly, since the liquefied gas fuel in a liquidstate remaining in each fuel injection nozzle can be more efficientlydelivered under pressure to the remaining fuel retrieving means by usinggravity, it is possible to achieve the effect and advantage of furtherreducing time taken to retrieve to the fuel tank the liquefied gas fuelremaining in the common rail, by the remaining fuel retrieving means.

The vapor-phase pressure delivery pipe preferably has a throttlingsection where the inside diameter of the vapor-phase pressure deliverypipe is partially reduced.

The vaporized liquefied gas fuel delivered from the vapor phase in thefuel tank is compressed to a far higher pressure by the throttlingsection, whereby the remaining liquefied gas fuel in a liquid state canbe delivered under a far higher pressure to the remaining fuelretrieving means. Accordingly, it is possible to achieve the effect andadvantage of further reducing time taken to retrieve the remainingliquefied gas fuel to the fuel tank.

An eleventh aspect of the invention provides a liquefied gas fuel supplydevice for a diesel engine according to the second or fourth aspect,characterized by further comprising: an oil separator for separating theliquefied gas fuel mixing with a lubricating oil in a cam chamber of theinjection pump which is a dedicated lubricating system separated from alubricating system for a diesel engine; a compressor for pressurizingthe liquefied gas fuel separated by the oil separator and delivering theliquefied gas fuel to the fuel tank; a low-pressure tank connected to asuction port of the compressor; a purge pipe causing the low-pressuretank and the overflow fuel pipe to communicate with each other; andpurge pipe opening/closing means capable of opening and closing thepurge pipe.

As described previously, the liquefied gas fuel has a nature differentfrom gases at room temperature and is low in viscosity, so that in theinjection pump, the liquefied gas fuel leaks into the cam chamber from aplunger of an injection pump element. For this reason, the camberchamber of the injection pump is formed as a dedicated lubricatingsystem separated from the lubricating system of the diesel engine, andthe liquefied gas fuel leaking into the cam chamber and mixing with thelubricating oil is separated by the oil separator and delivered underpressure to the fuel tank by the compressor. Accordingly, the liquefiedgas fuel leaking into the cam chamber can be decreased.

Since the low-pressure tank is connected to the suction port of thiscompressor, the inside of the low-pressure tank is maintained in alow-pressure state by the suction force of the compressor. When thepurge pipe opening/closing means is controlled to be opened and causethe injection system to communicate with the low-pressure tank, part ofthe liquefied gas fuel remaining in the injection system can be suckedand retrieved into the low-pressure tank via the overflow fuel pipe bythe negative pressure in the low-pressure tank maintained at a lowpressure by the suction port of the compressor. Then, the liquefied gasfuel retrieved into the low-pressure tank is delivered to the fuel tankwhile being vaporized by being sucked by the compressor.

Part of the liquefied gas fuel remaining in the injection system can besucked and retrieved into the low-pressure tank via the overflow fuelpipe by the negative pressure in the low-pressure tank maintained at alow pressure by using the compressor which delivers to the fuel tank theliquefied gas fuel separated from the lubricating oil in the cam chamberby the oil separator. Accordingly, part of the liquefied gas fuelremaining in the injection system can be reasonably retrieved through apassage different from the remaining fuel retrieving means. Accordingly,since the load on the remaining fuel retrieving means can be reduced, itis possible to achieve the effect and advantage of further reducing timetaken to retrieve to the fuel tank the liquefied gas fuel remaining inthe injection system by the remaining fuel retrieving means.

A twelfth aspect of the invention provides a liquefied gas fuel supplydevice for a diesel engine according to the eleventh aspect,characterized in that a check valve for holding pressure in thelow-pressure tank is disposed between the compressor and thelow-pressure tank.

Since the inside of the low-pressure tank is maintained at apredetermined pressure by the check valve, it is possible to achieve theeffect and advantage of constantly maintaining at a low pressure theinside of the low-pressure tank brought to a low-pressure state by beingsucked by the compressor.

A thirteenth aspect of the invention provides a liquefied gas fuelsupply device for a diesel engine according to the eleventh aspect,characterized in that the remaining fuel retrieving means includes: thefeed pipe opening/closing means and the fuel circulation pipeopening/closing means for switching a delivery port of the feed pipe toeither one of an inlet of a circulation passage of the aspirator and aninlet of the fuel gallery and causing the delivery port to communicatewith the either one; suction port opening/closing means for opening andclosing communication between the suction port of the aspirator and thefuel gallery as well as the overflow fuel pipe; and a liquefied gas fuelretrieving control section capable of executing control to switchcommunication provided by each of the feed pipe opening/closing meansand the fuel circulation pipe opening/closing means to the inlet of theaspirator, open the suction port opening/closing means, and form a flowpassage through which the liquefied gas fuel delivered from the feedpump is to be circulated to the fuel tank, as well as control to openthe vapor-phase pressure delivery pipe opening/closing means and, afterthe lapse of a predetermined time, close only the vapor-phase pressuredelivery pipe opening/closing means.

A ring-shaped flow of liquefied gas fuel along which the liquefied gasfuel in the fuel tank flows from the inlet to the outlet of theaspirator and again returns to the fuel tank is formed by the feed pipeopening/closing means and fuel circulation pipe opening/closing means aswell as the opening/closing operation of the suction portopening/closing means. At the same time, the vapor-phase pressuredelivery pipe opening/closing means is opened, and the liquefied gasfuel in a liquid state remaining in the fuel gallery and the overflowfuel pipe is forcedly delivered under pressure to the remaining fuelretrieving means by the pressure of the vapor phase in the fuel tank.Then, only the vapor-phase pressure delivery pipe opening/closing meansis closed after the lapse of a predetermined time, whereby the fuelgallery and the overflow fuel pipe are maintained in their low-pressurestates.

Namely, after the liquefied gas fuel in a liquid state remaining in thefuel gallery and the overflow fuel pipe has been delivered underpressure by the pressure of the vapor phase, only the vapor-phasepressure delivery pipe opening/closing means is closed. Accordingly, theinside of the fuel gallery and that of the overflow fuel pipe aremaintained in the lower-pressure states, whereby the vaporization of theliquefied gas fuel in a liquid state which slightly remains withoutbeing completely delivered under pressure can be accelerated.Accordingly, since the liquefied gas fuel in the fuel gallery and theoverflow fuel pipe can be retrieved to the fuel tank in a far shortertime, it is possible to achieve the effect and advantage of furtherreducing time taken to retrieve the liquefied gas fuel remaining in thefuel gallery and the overflow fuel pipe to the fuel tank by theremaining fuel retrieving means.

A fourteenth aspect of the invention provides a liquefied gas fuelsupply device for a diesel engine according to the thirteenth aspect,characterized in that the liquefied gas fuel retrieving control sectionis constructed to be able to execute control to open the purge pipeopening/closing means after closing the suction port opening/closingmeans.

After the stop of the diesel engine, the communication of the feed pipeopening/closing means and that of the fuel circulation pipeopening/closing means are switched to the inlet of the aspirator and thesuction port opening/closing means is opened, whereby a ring-shaped flowof liquefied gas fuel along which the liquefied gas fuel in the fueltank flows from the inlet to the outlet of the aspirator and againreturns to the fuel tank is formed, and the liquefied gas fuel remainingin the fuel gallery and the overflow fuel pipe is sucked from thesuction port of the aspirator and retrieved to the fuel tank. Then, thesuction of the remaining fuel by this aspirator is continued for apredetermined time, and when the remaining fuel still remains, thesuction port opening/closing means is closed to close the suction portof the aspirator. Then, the above-mentioned purge pipe opening/closingmeans is opened to cause the low-pressure tank and the overflow fuelpipe to communicate with each other, thereby rapidly sucking theremaining fuel by the negative pressure of the low-pressure tank. Afterthe liquefied gas fuel remaining in the injection system has beenretrieved to the fuel tank to some extent by the aspirator, the fuelremaining without being completely retrieved by the aspirator can berapidly sucked and retrieved by the negative pressure of thelow-pressure tank. Accordingly, it is possible to achieve the effect andadvantage of further reducing time taken to retrieve liquefied gas fuelremaining in the injection system after the stop of the diesel engine.

A fifth aspect of the invention provides a liquefied gas fuel supplydevice for a diesel engine according to the third aspect or the fourthaspect, characterized in that the remaining fuel retrieving meansincludes: feed pipe opening/closing means for opening and closingcommunication of the feed pipe on the same side as the injection pumpwith respect to the branch point between the feed pipe and the fuelcirculation pipe; fuel circulation pipe opening/closing means foropening and closing an inlet of the aspirator; suction portopening/closing means for opening and closing a communication pipebetween the suction port of the aspirator and the fuel gallery as wellas the overflow fuel pipe; and a liquefied gas fuel retrieving controlsection for executing control to open and close the feed pump, the feedpipe opening/closing means, the fuel circulation pipe opening/closingmeans, and the suction port opening/closing means. The liquefied gasfuel retrieving control section is constructed to be able to execute,after the stop of the diesel engine, control to close the feed pipeopening/closing means and cut off supply of liquefied gas fuel to thefuel gallery, and control to circulate the liquefied gas fuel deliveredfrom the feed pump to the fuel tank via the fuel circulation pipe whilecausing the suction port of the aspirator to communicate with the fuelgallery as well as the overflow fuel pipe, by executing control to openthe fuel circulation pipe opening/closing means and the suction portopening/closing means.

After the stop of the diesel engine, the feed pipe opening/closing meansis controlled to be closed and cut off the supply of liquefied gas fuelto the fuel gallery, and the fuel circulation pipe opening/closing meansand the suction port opening/closing means are controlled to be openedand form a circulation passage along which the liquefied gas fueldelivered from the feed pump is circulated to the fuel tank via the fuelcirculation pipe with the suction port of the aspirator communicatingwith the fuel gallery as well as the overflow fuel pipe. The liquefiedgas fuel delivered from the feed pipe flows into the fuel circulationpipe, then flows from the inlet to the outlet of the aspirator, andagain returns to the fuel tank. A ring-shaped flow of liquefied gas fuelincluding the aspirator is formed and suction force is produced in thesuction port of the aspirator. The liquefied gas fuel remaining in thefuel gallery and the overflow fuel pipe is sucked from the suction portof the aspirator, and is retrieved to the fuel tank together withliquefied gas fuel flowing from the inlet to the outlet of theaspirator.

In this manner, the fuel circulation pipe opening/closing means capableof opening and closing the inlet of the aspirator is disposed in thefuel circulation pipe, and the feed pipe opening/closing means capableof opening and closing the communication of the feed pipe on the sameside as the injection pump with respect to the branch point between thefeed pipe and the fuel circulation pipe is disposed in the feed pipe,and the liquefied gas fuel retrieving control section executes controlto open and close the fuel circulation pipe opening/closing means andthe feed pipe opening/closing means. Therefore, the opening and closingof the fuel circulation pipe on the side of the inlet of the aspiratorand the opening and closing of the feed pipe on the same side as theinjection pump with respect to the branch point between the feed pipeand the fuel circulation pipe can be independently performed.

Accordingly, according to the liquefied gas fuel supply device for adiesel engine according to the fifteenth aspect of the invention, theliquefied gas fuel retrieving control section can execute control toopen and close the feed pipe opening/closing means and the fuelcirculation pipe opening/closing means, whereby it is possible toachieve the effect and advantage achieved by the third aspect or thefourth aspect of the invention.

A sixteenth aspect of the invention provides a liquefied gas fuel supplydevice for a diesel engine according to the fifteenth aspect,characterized in that the liquefied gas fuel retrieving control sectionis constructed to be able to execute control to hold the liquefied gasfuel in the state of being charged in the feed pipe between the feedpipe opening/closing means and the check valve, while continuing controlto close the feed pipe opening/closing means, after having retrieving tothe fuel tank the liquefied gas fuel remaining in the fuel gallery andthe overflow fuel pipe.

In this manner, since the liquefied gas fuel is held in the state ofbeing charged in the feed pipe between the feed pipe opening/closingmeans and the check valve, with the feed pipe opening/closing meanscontrolled to be closed, after the liquefied gas fuel remaining in thefuel gallery and the overflow fuel pipe has been retrieved to the fueltank, it is possible to reduce the amount of liquefied gas fuel to beretrieved by the remaining fuel retrieving means after the stop of thediesel engine, and it is also possible to reduce the amount of liquefiedgas fuel to be charged into the injection system at the starting time ofthe diesel engine.

A seventeenth aspect of the invention provides a liquefied gas fuelsupply device for a diesel engine according to the fifteenth aspect,characterized in that in the remaining fuel retrieving means, theaspirator and the fuel circulation pipe opening/closing means aredisposed immediately close to the fuel tank.

In this manner, by making the length of the fuel circulation pipe asshort as possible, it is possible to minimize the flow passageresistance of the fuel circulation pipe. Accordingly, it is possible tominimize a decrease in the flow rate of liquefied gas fuel flowing inthe circulation passage, and it is possible to minimize a decrease inthe flow rate of suction force produced in the suction port of theaspirator, whereby it is possible to further improve the efficiency ofretrieving of remaining fuel by the aspirator.

An eighteenth aspect of the invention provides a liquefied gas fuelsupply device for a diesel engine according to the fifteenth aspect,characterized in that in the remaining fuel retrieving means, the feedpipe opening/closing means is disposed in the feed pipe in the vicinityof an inlet of the fuel gallery, and the check valve is disposedimmediately close to the branch point between the feed pipe and the fuelcirculation pipe.

In this manner, the feed pipe opening/closing means is disposed in thevicinity of the inlet of the fuel gallery of the injection pump, and thecheck valve is disposed immediately close to the branch point betweenthe feed pipe and the fuel circulation pipe. Accordingly, by closing thefeed pipe opening/closing means, the liquefied gas fuel can be held inthe state of being charged in the feed pipe between the vicinity of theinlet of the fuel gallery of the injection pump and the close vicinityof the branch point between the feed pipe and the fuel circulation pipe.In addition, since the liquefied gas fuel is also held in the state ofbeing charged between the fuel tank and the check valve, when theliquefied gas fuel is to be charged into the injection system at thestarting time of the diesel engine, the liquefied gas fuel can start tobe charged into the fuel gallery of the injection pump at approximatelythe same time as the start of charging. Accordingly, it is possible tofurther reduce time taken to charge the liquefied gas fuel into theinjection system at the starting time of the diesel engine.

A nineteenth aspect of the invention provides a liquefied gas fuelsupply device for a diesel engine according to the fifth aspect,characterized in that the liquefied gas fuel retrieving control sectionis constructed to be able to execute control to open the vapor-phasepressure delivery pipe opening/closing means and deliver vapor-phasepressure in the fuel tank to the fuel gallery and the overflow fuelpipe.

By opening the vapor-phase pressure delivery pipe opening/closing means,it is possible to forcedly deliver the liquefied gas fuel remaining inthe fuel gallery and the overflow fuel pipe to the remaining fuelretrieving means by the pressure of the vapor phase in the fuel tank.Accordingly, it is possible to achieve the effect and advantage offurther reducing time taken to retrieve the liquefied gas fuel remainingin the fuel gallery and the overflow fuel pipe to the fuel tank by theremaining fuel retrieving means.

A twentieth aspect of the invention provides a liquefied gas fuel supplydevice for a diesel engine according to the eleventh aspect,characterized in that the liquefied gas fuel retrieving control sectionis constructed to be able to execute, after the stop of a diesel engine,control to close the feed pipe opening/closing means and cut off supplyof liquefied gas fuel to the fuel gallery, and execute, after stoppingthe feed pump with the suction port opening/closing means closed,control to open the purge pipe opening/closing means and suck theliquefied gas fuel remaining in the fuel gallery and the overflow fuelpipe to the low-pressure tank.

After the stop of the diesel engine, the feed pipe opening/closing meansis controlled to be closed and cut off the supply of the liquefied gasfuel to the fuel gallery, and when the feed pump is stopped with thesuction port opening/closing means closed, the fuel gallery and theoverflow fuel pipe are separated from the feed pipe and the aspirator.Then, the above-mentioned purge pipe opening/closing means is opened tocause the low-pressure tank and the overflow fuel pipe to communicatewith each other, and the fuel remaining in the fuel gallery and theoverflow fuel pipe is sucked by the negative pressure of thelow-pressure tank. In this manner, by retrieving the fuel remaining inthe fuel gallery and the overflow fuel pipe by the negative pressure ofthe low-pressure tank, it is possible to achieve the effect andadvantage of further reducing time taken to retrieve the liquefied gasfuel remaining in the injection system by the aspirator after the stopof the diesel engine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a first embodiment of a DME fuelsupply device according to the invention;

FIG. 2 is a schematic diagram showing the stopped state of the DME fuelsupply device according to the first embodiment of the invention;

FIG. 3 is a schematic diagram showing the state of the DME fuel supplydevice according to the first embodiment of the invention during fuelcharging as well as during operation;

FIG. 4 is a schematic diagram showing the state of the DME fuel supplydevice according to the first embodiment of the invention during theretrieving of remaining fuel, and shows the state in which DME fuel isbeing retrieved by an aspirator (vapor-phase substitution);

FIG. 5 is a schematic diagram showing the state of the DME fuel supplydevice according to the first embodiment of the invention during theretrieving of remaining fuel, and shows the state in which DME fuel isbeing sucked into a low-pressure tank;

FIG. 6 is a schematic diagram showing a second embodiment of the DMEfuel supply device according to the invention, and shows a DME fuelsupply device for a common rail diesel engine in which a vapor-phasepressure delivery pipe is connected to a common rail;

FIG. 7 is a schematic diagram showing a third embodiment of the DME fuelsupply device according to the invention, and shows a DME fuel supplydevice for a common rail diesel engine in which the vapor-phase pressuredelivery pipe is connected to an injection pipe;

FIG. 8 is a schematic diagram showing a fourth embodiment of the DMEfuel supply device according to the invention;

FIG. 9 is a schematic diagram showing a fifth embodiment of the DME fuelsupply device according to the invention;

FIG. 10 is a schematic diagram showing the stopped state of the DME fuelsupply device according to the fifth embodiment of the invention;

FIG. 11 is a schematic diagram showing the state of the DME fuel supplydevice according to the fifth embodiment of the invention during fuelcharging as well as during operation;

FIG. 12 is a schematic diagram showing the state of the DME fuel supplydevice according to the fifth embodiment of the invention during theretrieving of remaining fuel, and shows the state in which DME fuel isbeing retrieved by the aspirator (vapor-phase substitution);

FIG. 13 is a schematic diagram showing the state of the DME fuel supplydevice according to the fifth embodiment of the invention during theretrieving of remaining fuel, and shows the state in which DME fuel isbeing sucked into the low-pressure tank;

FIG. 14 is a schematic diagram showing a sixth embodiment of the DMEfuel supply device according to the invention, and shows a DME fuelsupply device for a common rail diesel engine in which the vapor-phasepressure delivery pipe is connected to a common rail; and

FIG. 15 is a schematic diagram showing a seventh embodiment of the DMEfuel supply device according to the invention, and shows a DME fuelsupply device for a common rail diesel engine in which the vapor-phasepressure delivery pipe is connected to the injection pipe.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the invention of the present application will bedescribed below with reference to the accompanying drawings.

First, a schematic structure of a liquefied gas fuel supply device for adiesel engine will be described. FIG. 1 is a schematic diagram showing afirst embodiment of a liquefied gas fuel supply device for a dieselengine according to the invention of the present application.

A liquefied gas fuel supply device 100 which supplies liquefied gas fuelto a diesel engine has an injection pump 1. Representative examples ofliquefied gas fuel are DME and high cetane number LP gas (LP gas towhich a cetane number improver is added) having a cetane number ofapproximately 40-55, desirably, 50 or higher. In embodiments which willbe described later, reference will be made to examples in which DME isused as liquefied gas fuel. Incidentally, when high cetane number LP gasis used, a known material such as a nitric ester, a nitrite and anorganic peroxide are used as a cetane number improver. A specific cetanenumber improver is DTBP (Di-tertiary butyl peroxide) or 2HEN(2-Ethylhexylnitrate). In addition, since LP gas is low in lubricationability compared to light oil, a known alkyl ester is desirably added toLP gas as a lubrication improver.

The injection pump 1 has the same number of injection pump elements 2 asthe number of cylinders which the diesel engine has. A feed pump 51pressurizes DME fuel reserved in a fuel tank 4 to a predeterminedpressure and delivers the DME fuel into a feed pipe 5. A DME fueldelivery port 41 of the fuel tank 4 is provided below the level of aliquid phase 4 a in the fuel tank 4, and the feed pump 51 is disposed inthe vicinity of the DME fuel delivery port 41 of the fuel tank 4. TheDME fuel delivered into the feed pipe 5 is filtered by a filter 52, andis delivered to the injection pump 1 via a three-way solenoid valve 71.During an injection state (during the operation of the diesel engine),the three-way solenoid valve 71 is ON and permitted to communicate inthe directions shown in FIG. 1.

A cam chamber 12 in the injection pump 1 is a dedicated lubricatingsystem separated from a lubricating system for the diesel engine, and anoil separator 13 separates DME fuel and a lubricating oil from thelubricating oil in the cam chamber 12 that is mixed with DME fuel whichhas leaked into the cam chamber 12 in the injection pump 1, and returnsthe lubricating oil to the cam chamber 12. The DME fuel separated by theoil separator 13 is delivered to a compressor 16 via a check valve(nonreturn valve) 14 which prevents the pressure inside the cam chamber12 from becoming not higher than atmospheric pressure, and the DME fuel,after having been pressurized by the compressor 16, is returned to thefuel tank 4 via a check valve (nonreturn valve) 15 and a cooler 42. Thecheck valve 15 is provided for preventing DME fuel from flowing back tothe cam chamber 12 from the fuel tank 4 during the stop of the dieselengine. The compressor 16 is a compressor which uses a cam in the camchamber 12 as its driving force source. Accordingly, a more power-savingDME fuel supply device 100 can be realized.

The DME fuel which has been pressurized to the predetermined pressure bythe feed pump 51 and delivered from the fuel tank 4 is delivered underpressure by a predetermined amount at predetermined timing from each ofthe injection pump elements 2 of the injection pump 1 to a fuelinjection nozzle 9 disposed in each of the cylinders of the dieselengine via an injection pipe 3. An overflow fuel pipe 81 is providedwith an overflow valve 82 which maintains the pressure of DME fuel in afuel gallery 11 at a predetermined pressure and regulates the flowingdirection of DME fuel in only the direction in which overflowed DME fuelis allowed to return to the fuel tank 4. The DME fuel which hasoverflowed from the injection pump 1 passes through the overflow fuelpipe 81 and is returned to the fuel tank 4 via the overflow valve 82 andthe cooler 42. The DME fuel which has overflowed from each of the fuelinjection nozzles 9 is returned to the fuel tank 4 via a nozzle returnpipe 6, an overflow return pipe 8, and the cooler 42.

The DME fuel supply device 100 also has “remaining fuel retrievingmeans” for retrieving to the fuel tank 4 the DME fuel remaining in thefuel gallery 11 in the injection pump 1 as well as in the overflow fuelpipe 81 during the stop of the diesel engine. The “remaining fuelretrieving means” has an aspirator 7, the three-way solenoid valve 71, atwo-way solenoid valve 72 and a DME fuel retrieving control section 10.The DME fuel retrieving control section 10 detects the operating/stoppedstate of the diesel engine (the injection/non-injection state of the DMEfuel supply device 100), and executes ON/OFF control on the three-waysolenoid valve 71, the two-way solenoid valve 72 and the feed pump 51according to each of the states. During the stop of the diesel engine,the DME fuel retrieving control section 10 executes control to retrievethe DME fuel remaining in the fuel gallery 11 and the overflow fuel pipe81.

The aspirator 7 has an inlet 7 a, an outlet 7 b and a suction port 7 c.The inlet 7 a and the outlet 7 b straightforwardly communicate with eachother, and the suction port 7 c is branched in an approximatelyperpendicular direction from the communication passage between the inlet7 a and the outlet 7 b. The outlet side of a communication passage whichis permitted to communicate when the three-way solenoid valve 71 is OFFis connected to the inlet 7 a, and the outlet 7 b is connected to apassage to the fuel tank 4 via the cooler 42. The suction port 7 c isconnected to the two-way solenoid valve 72 serving as suction portopening/closing means which is closed in an OFF state during theinjection state (during the operation of the diesel engine). FIG. 1shows the vertical positional relationship between constituent elements(as in the following drawings), and the aspirator 7 is disposed at aposition lower than the overflow fuel pipe 81.

The “remaining fuel retrieving means” also has a vapor-phase pressuredelivery pipe 73 and a vapor-phase pressure delivery pipeopening/closing solenoid valve 74 for opening and closing thecommunication of the vapor-phase pressure delivery pipe 73, as means forconnecting an outlet for a vapor phase 4 b in the fuel tank 4 (avapor-phase delivery port 43) and an inlet side of the fuel gallery 11of the injection pump 1. The vapor-phase pressure delivery pipe 73 has athrottling portion 75 whose inside diameter is partially reduced, andthe vapor-phase pressure delivery pipe opening/closing solenoid valve 74is disposed at a position higher than the fuel gallery 11 of theinjection pump 1. The vapor-phase pressure delivery pipe opening/closingsolenoid valve 74 is ON/OFF controlled by the DME fuel retrievingcontrol section 10 so that the communication of the vapor-phase pressuredelivery pipe 73 is opened when the vapor-phase pressure delivery pipeopening/closing solenoid valve 74 is in its ON control state.

The DME fuel supply device 100 further has a low-pressure tank 17 havinga hermetically sealed structure smaller in capacity than the fuel tank4. The low-pressure tank 17 is constructed so that its internal pressureis brought to a low-pressure state when the low-pressure tank 17 issucked by the compressor 16, and so that the low-pressure state ismaintained by a check valve 171 even when the compressor 16 stops. Thelow-pressure tank 17 communicates with the overflow fuel pipe 81upstream of the overflow valve 82 through a purge pipe 19, and the purgepipe 19 is provided with a purge pipe opening/closing solenoid valve 18capable of opening and closing the purge pipe 19. The purge pipeopening/closing solenoid valve 18 is controlled by the DME fuelretrieving control section 10, and during the stop of the diesel engine,the purge pipe opening/closing solenoid valve 18 is turned on andbrought to its open state so that the low-pressure tank 17 and theoverflow fuel pipe 81 communicate with each other, while during theoperation of the diesel engine, the purge pipe opening/closing solenoidvalve 18 is turned off and brought to its closed state so that thecommunication between the low-pressure tank 17 and the overflow fuelpipe 81 is cut off.

Next, the states of control of each of the three-way solenoid valve 71,the two-way solenoid valve 72, the vapor-phase pressure delivery pipeopening/closing solenoid valve 74, the purge pipe opening/closingsolenoid valve 18, and the feed pump 51 by the DME fuel retrievingcontrol section 10 in the DME fuel supply device 100 during stop, fuelcharging, engine operation and retrieving of remaining fuel will bedescribed with reference to the corresponding drawings.

FIG. 2 is a schematic diagram showing the stopped state of the DME fuelsupply device 100 according to the invention of the present application.

During stop, the DME fuel retrieving control section 10 executes OFFcontrol on all of the three-way solenoid valve 71, the two-way solenoidvalve 72, the vapor-phase pressure delivery pipe opening/closingsolenoid valve 74, the purge pipe opening/closing solenoid valve 18, andthe feed pump 51. During the OFF control, the feed pump 51 is stopped,and the three-way solenoid valve 71 forms a passage which permits thefeed pipe 5 to communicate with the inlet 7 a of the aspirator 7 via afuel circulation pipe 53, and the two-way solenoid valve 72, thevapor-phase pressure delivery pipe opening/closing solenoid valve 74 andthe purge pipe opening/closing solenoid valve 18 are brought to theirclosed states.

FIG. 3 is a schematic diagram showing the state of the DME fuel supplydevice 100 according to the invention of the present application duringfuel charging as well as during operation.

During the fuel charging of charging DME fuel into an injection systemsuch as the fuel gallery 11 from the stopped state, the DME fuelretrieving control section 10 executes ON control on the three-waysolenoid valve 71, and then executes ON control on the feed pump 51. Thethree-way solenoid valve 71 is ON controlled so that the communicationpassage of the feed pipe 5 switches from the inlet 7 a of the aspirator7 to the fuel gallery 11 and the DME fuel of the fuel tank 4 isdelivered under pressure to the fuel gallery 11 by the feed pump 51(symbol A). When the DME fuel is charged into the fuel gallery 11, theinjection pipe 3 and the overflow fuel pipe 81 (the fuel-gallery side ofthe overflow valve 82) (symbol B), the diesel engine is brought to itsoperable state. When the diesel engine in this state is started andreaches its operating state, the cam in the cam chamber 12 of theinjection pump 1 rotates in conjunction with the operation of the dieselengine, thereby operating the compressor 16. As described above, DMEfuel which has entered the cam chamber 12 is separated by the oilseparator 13 and is then returned to the fuel tank 4 by being sucked bythe compressor 16 (symbol C). The inside of the low-pressure tank 17 isalso sucked by the compressor 16 and maintained in the low-pressurestate.

FIG. 4 is a schematic diagram showing the state of the DME fuel supplydevice 100 according to the invention of the present application duringthe retrieving of remaining fuel, and shows the state in which DME fuelis being retrieved by the aspirator 7 (vapor-phase substitution).

After the diesel engine has been stopped, in order to retrieve to thefuel tank the DME fuel remaining in the fuel gallery 11, the injectionpipe 3 and the overflow fuel pipe 81, the DME fuel retrieving controlsection 10 turns off the three-way solenoid valve 71 to form thecommunication passage from the feed pipe 5 to the inlet 7 a of theaspirator 7, as well as turns on the two-way solenoid valve 72 toprovide communication between the overflow fuel pipe 81 upstream of theoverflow valve 82 and the suction port 7 c of the aspirator 7.Accordingly, the DME fuel delivered from the feed pump 51 is deliverednot to the injection pump 1 but to the aspirator 7, passed from theinlet 7 a to the outlet 7 b, returned to the fuel tank 4 via theoverflow fuel pipe 81 downstream of the overflow valve 82, the overflowreturn pipe 8 and cooler 42 and again delivered from the feed pump 51 tothe aspirator 7. Namely, DME fuel liquid is circulated via the aspirator7 (symbol D). The DME fuel remaining in the fuel gallery 11 in theinjection pump 1 as well as in the overflow fuel pipe 81 upstream of theoverflow valve 82 is vaporized, i.e., substituted by a vapor phase, bysuction force produced by the flow of DME fuel which flows from theinlet 7 a to the outlet 7 b through the circulation of the remaining DMEfuel, and is sucked through the suction port 7 c and absorbed into theDME fuel flowing from the inlet 7 a to the outlet 7 b, and is retrievedto the fuel tank 4 (symbol E).

At the same time that the DME fuel of the fuel gallery 11 and theoverflow fuel pipe 81 is retrieved to the fuel tank 4 by being sucked bythe aspirator, the DME fuel retrieving control section 10 also executesON control on the vapor-phase pressure delivery pipe opening/closingsolenoid valve 74 and brings the vapor-phase pressure delivery pipe 73which connects the vapor phase 4 b of the fuel tank 4 and the inlet ofthe fuel gallery 11, into a communicating state. The DME fuel in aliquid state remaining in the fuel gallery 11 and the overflow fuel pipe81 is delivered under pressure to the suction port 7 c of the aspirator7 by the high pressure of the vapor phase 4 b (symbol F). In addition,this pressure is compressed to a far higher pressure by the throttlingsection 75 where the inside diameter of the vapor-phase pressuredelivery pipe 73 is partially reduced, whereby the remaining DME fuelcan be delivered under pressure by a far higher pressure.

Accordingly, since the DME fuel in a liquid state is delivered underpressure to the suction port 7 c of the aspirator 7 by using thepressure of the vapor phase 4 b, it is possible to reduce time taken toretrieve the DME fuel remaining in the fuel gallery 11 and the overflowfuel pipe 81. The DME fuel retrieving control section 10, after thelapse of a predetermined time, closes only the vapor-phase pressuredelivery pipe opening/closing solenoid valve 74 and cuts off thecommunication with the vapor phase 4 b in a high-pressure state.Accordingly, since the inside of the fuel gallery 11 and that of theoverflow fuel pipe 81 can be brought into lower-pressure states, thevaporization of the DME fuel in a liquid state which remains withoutbeing delivered under pressure by vapor phase pressure can beaccelerated, whereby it is possible to further reduce time taken toretrieve the remaining DME fuel by the “remaining fuel retrievingmeans”.

In addition, in the DME fuel supply device 100 according to theinvention of the present application, since the aspirator 7 is disposedat a position lower than the fuel gallery 11 and the overflow fuel pipe81, the DME fuel remaining in the fuel gallery 11 and the overflow fuelpipe 81 is retrieved to the fuel tank 4 by a combined force of gravityand the suction force produced in the suction port 7 c of the aspirator7. Accordingly, it is possible to more efficiently retrieve the DME fuelremaining in the injection system by using gravity, and it is possibleto further reduce time taken to retrieve the DME fuel in the injectionsystem to the fuel tank 4 after the stop of the diesel engine.

In addition, since the vapor-phase pressure delivery pipeopening/closing solenoid valve 74 is disposed at a position higher thanthe fuel gallery 11, the DME fuel in a liquid state remaining in thefuel gallery 11 and the overflow fuel pipe 81 is forcedly deliveredunder pressure to the suction port 7 c of the aspirator 7 by a combinedforce of gravity and the pressure of the vapor phase 4 b in the fueltank 4. Accordingly, gravity can be used to more efficiently deliverunder pressure the DME fuel in a liquid state remaining in the fuelgallery 11 and the overflow fuel pipe 81 to the suction port 7 c of theaspirator 7, whereby it is possible to further reduce time taken toretrieve the DME fuel remaining in the fuel gallery 11 and the overflowfuel pipe 81 to the fuel tank 4.

FIG. 5 is a schematic diagram showing the state of the DME fuel supplydevice 100 according to the invention of the present application duringthe retrieving of remaining fuel, and shows the state in which DME fuelis being sucked into the low-pressure tank 17.

After the DME fuel retrieving control section 10 has retrieved the DMEfuel remaining in the fuel gallery 11 and the overflow fuel pipe 81, bymeans of the aspirator 7 for a predetermined time, the DME fuelretrieving control section 10 executes OFF control to stop the feed pump51, and executes OFF control on the two-way solenoid valve 72 to cut offthe communication between the overflow fuel pipe 81 and the suction port7 c of the aspirator 7. Then, the DME fuel retrieving control section 10executes ON control on the purge pipe opening/closing solenoid valve 18to provide communication between the low-pressure tank 17 maintained inan approximately constant low pressure state and the overflow fuel pipe81. The residual DME fuel remaining in the overflow fuel pipe 81 issucked and retrieved to the low-pressure tank 17 by the negativepressure in the low-pressure tank 17 (symbol G). When the diesel engineagain starts and the compressor 16 is activated, the DME fuel suckedinto the low-pressure tank 17 is sucked by the compressor 16 and isretrieved to the fuel tank 4 through the overflow return pipe 8 (symbolH).

Accordingly, since the purge pipe opening/closing solenoid valve 18 isturned on after the DME fuel remaining in the fuel gallery 11 and theoverflow fuel pipe 81 has been retrieved to some extent by the aspirator7, the DME fuel remaining without being completely retrieved by theaspirator 7 can be rapidly sucked and retrieved into the low-pressuretank 17. Accordingly, it is possible to further reduce time taken toretrieve DME fuel by the “remaining fuel retrieving means”.

In this manner, it is possible to reduce time taken to retrieve the DMEfuel in the injection system to the fuel tank 4 after the stop of thediesel engine.

As another embodiment, there is provided the DME fuel supply device 100for a common rail diesel engine in which a common rail is providedbetween the injection pump 1 and the injection nozzle 9 in theabove-mentioned first embodiment.

FIG. 6 is a schematic diagram showing a second embodiment of the DMEfuel supply device 100 according to the invention of the presentapplication, and shows the DME fuel supply device 100 for a common raildiesel engine in which the vapor-phase pressure delivery pipe 73 isconnected to a common rail. FIG. 7 is a schematic diagram showing athird embodiment of the DME fuel supply device 100 according to theinvention of the present application, and shows the DME fuel supplydevice 100 for a common rail diesel engine in which the vapor-phasepressure delivery pipe 73 is connected to the injection pipe 3.

In the above-mentioned first embodiment, the injection nozzle 9 isconstructed to be opened for injection of DME fuel by the pressure ofDME fuel delivered under pressure from the injection pump 1 to theinjection pipe 3. For this reason, when the injection pipe 3 isconnected to the vapor-phase pressure delivery pipe 73, there is apossibility that the pressure in the injection pipe 3 becomes unstable,and there is a risk that the fuel injection characteristics of theinjection nozzle 9 become unstable. Therefore, the vapor-phase pressuredelivery pipe 73 cannot be connected to the injection pipe 3.

On the other hand, the DME fuel supply device 100 for a common raildiesel engine has a construction in which DME fuel is delivered underpressure from the injection pump 1 to a common rail 91 and the DME fuelin the common rail 91 maintained in a given high-pressure state isdelivered to each injection nozzle 9. For this reason, the common raildiesel engine adopts an electromagnetic type of valve opening mechanism.This injection nozzle 9 is not easily influenced by pressure variationsin the injection pipe 3.

Accordingly, in the DME fuel supply device 100 for a common rail dieselengine, as shown in FIG. 6, the vapor-phase pressure delivery pipe 73can be connected to the common rail 91 (embodiment 2). Accordingly,after the stop of the diesel engine while the DME fuel remaining in thecommon rail 91, the fuel gallery 11 and the overflow fuel pipe 81 isbeing retrieved to the fuel tank 4 by the above-mentioned “remainingfuel retrieving means”, the DME fuel in a liquid state remaining in thecommon rail 91 can be forcedly delivered under pressure to the aspirator7 by the pressure of the vapor phase 4 b in the fuel tank 4.Accordingly, it is possible to further reduce time taken to retrieve theDME fuel remaining in the common rail 91 to the fuel tank 4 by means ofthe aspirator 7. In addition, since the vapor-phase pressure deliverypipe opening/closing solenoid valve 74 which opens and closes thevapor-phase pressure delivery pipe 73 is disposed at a position higherthan the common rail 91, the DME fuel in a liquid state remaining in thecommon rail 91 can be forcedly delivered under pressure to the aspirator7 by a combined force of gravity and vapor phase pressure. As to thesecond embodiment (FIG. 6) and the third embodiment (FIG. 7), thedescription of sections which have the same constructions as thecorresponding ones of the first embodiment is omitted herein.

Furthermore, in the DME fuel supply device 100 for a common rail dieselengine, as shown in FIG. 7, the vapor-phase pressure delivery pipe 73may also be connected to the vicinity of the injection nozzle 9 of theinjection pipe 3 (the inlet side of the injection nozzle 9) (embodiment3). If the vapor-phase pressure delivery pipe 73 is connected in thismanner to the vicinity of the injection nozzle 9 of the injection pipe 3disposed at a position far higher than the common rail 91, not only theDME fuel remaining in the common rail 91 but also the DME fuel remainingin the injection pipe 3 can be delivered under pressure directly to theaspirator 7 by vapor phase pressure. Accordingly, it is possible tofurther reduce time taken to retrieve the DME fuel remaining in thecommon rail 91 and the injection pipe 3 to the fuel tank 4 by means ofthe aspirator 7. In addition, since the vapor-phase pressure deliverypipe opening/closing solenoid valve 74 which opens and closes thevapor-phase pressure delivery pipe 73 is disposed at a position higherthan the injection pipe 3, the DME fuel in a liquid state remaining inthe injection pipe 3 can be more efficiently forcedly delivered underpressure to the aspirator 7 by a combined force of gravity and vaporphase pressure.

FIG. 8 shows the case in which the three-way solenoid valve 71 in thefirst embodiment shown in FIG. 1 is divided into a two-way solenoidvalve 711 which serves as feed pipe opening/closing means and a two-waysolenoid valve 712 which serves as fuel circulation pipe opening/closingmeans (fourth embodiment). Specifically, a check valve 713 is disposedbetween a position where the fuel circulation pipe 53 is branched fromthe feed pipe 5 and the two-way solenoid valve serving as feed pipeopening/closing means (hereinafter referred to as the “feed pipeopening/closing solenoid valve”) 711, and serves to prevent liquefiedgas fuel from flowing back from the injection pump 1. Furthermore, thetwo-way solenoid valve serving as fuel circulation pipe opening/closingmeans for opening and closing the flow passage of the fuel circulationpipe 53 (hereinafter referred to as the “fuel circulation pipeopening/closing solenoid valve”) 712 is disposed in the fuel circulationpipe 53. The other sections are identical in construction to thecorresponding one of the first embodiment, and the same description isomitted herein. In this manner, the three-way solenoid valve 71 isdivided into the feed pipe opening/closing solenoid valve 711 and thefuel circulation pipe opening/closing solenoid valve 712, and further,the check valve 713 is disposed, whereby each of the values 711 and 712can be individually controlled to be opened and closed, and the range ofcontrol modes can be made wide. Further effects and advantages of thecheck valve 713 will become apparent from the description of embodimentswhich will be mentioned below.

FIG. 9 is a schematic diagram showing a fifth embodiment of the DME fuelsupply device according to the invention.

The DME fuel supply device 100 for supplying DME fuel to a diesel engineincludes an injection pump 1. The injection pump 1 has the same numberof injection pump elements 2 as the number of cylinders which the dieselengine has. The feed pump 51 pressurizes DME fuel reserved in the fueltank 4 to a predetermined pressure and delivers the DME fuel into thefeed pipe 5. The DME fuel delivery port 41 of the fuel tank 4 isprovided below the level of the liquid phase 4 a in the fuel tank 4, andthe feed pump 51 is disposed in the vicinity of the DME fuel deliveryport 41 of the fuel tank 4. The DME fuel delivered into the feed pipe 5is filtered by the filter 52, and is delivered to the injection pump 1via the check valve 713 and the feed pipe opening/closing solenoid valve711. During an injection state (during the operation of the dieselengine), the feed pipe opening/closing solenoid valve 711 is ON in anopened state, and the feed pipe 5 is in its communicating state. Thecheck valve 713 prevents DME fuel from flowing back from the injectionpump 1 to the fuel tank 4.

The cam chamber 12 in the injection pump 1 is a dedicated lubricatingsystem separated from a lubricating system for the diesel engine, andthe oil separator 13 separates DME fuel and a lubricating oil from thelubricating oil in the cam chamber 12 that is mixed with DME fuel whichhas leaked into the cam chamber 12 in the injection pump 1, and returnsthe lubricating oil to the cam chamber 12. The DME fuel separated by theoil separator 13 is delivered to the compressor 16 via the check valve(nonreturn valve) 14 which prevents the pressure inside the cam chamber12 from becoming not higher than atmospheric pressure, and the DME fuel,after having been pressurized by the compressor 16, is returned to thefuel tank 4 via the check valve (nonreturn valve) 15 and the cooler 42.The check valve 15 is provided for preventing DME fuel from flowing backto the cam chamber 12 from the fuel tank 4 during the stop of the dieselengine. The compressor 16 is a compressor which uses the cam in the camchamber 12 as its driving force source. Accordingly, a more power-savingDME fuel supply device 100 can be realized.

The DME fuel which has been pressurized to the predetermined pressure bythe feed pump 51 and delivered from the fuel tank 4 is delivered underpressure by a predetermined amount at predetermined timing from each ofthe injection pump elements 2 of the injection pump 1 to the fuelinjection nozzle 9 disposed in each of the cylinders of the dieselengine via the injection pipe 3. The overflow fuel pipe 81 is providedwith the overflow valve 82 which maintains the pressure of DME fuel inthe fuel gallery 11 at a predetermined pressure and regulates theflowing direction of DME fuel in only the direction in which overflowedDME fuel is allowed to return to the fuel tank 4. The DME fuel which hasoverflowed from the injection pump 1 passes through the overflow fuelpipe 81 and is returned to the fuel tank 4 via the overflow valve 82 andthe cooler 42. The DME fuel which has overflowed from each of the fuelinjection nozzles 9 is returned to the fuel tank 4 via the nozzle returnpipe 6, the overflow return pipe 8, and the cooler 42.

The DME fuel supply device 100 also has the “remaining fuel retrievingmeans” for retrieving to the fuel tank 4 the DME fuel remaining in thefuel gallery 11 in the injection pump 1 as well as in the overflow fuelpipe 81 (hereinafter referred to also as the injection system) duringthe stop of the diesel engine. The “remaining fuel retrieving means” hasthe aspirator 7, the fuel circulation pipe 53, the fuel circulation pipeopening/closing solenoid valve 712, the feed pipe opening/closingsolenoid valve 711, the suction port opening/closing solenoid valve 72,and the DME fuel retrieving control section 10.

The aspirator 7 has the inlet 7 a, the outlet 7 b and the suction port 7c. The inlet 7 a and the outlet 7 b straightforwardly communicate witheach other, and the suction port 7 c is branched in an approximatelyperpendicular direction from the communication passage between the inlet7 a and the outlet 7 b. When DME fuel flows from the inlet 7 a to theoutlet 7 b, suction force is produced in the suction port 7 c. FIG. 9shows the vertical positional relationship between constituent elements(as in the following drawings), and the aspirator 7 is disposed at aposition lower than the overflow fuel pipe 81. The fuel circulation pipe53 is branched from the feed pipe 5 of the vicinity of a delivery portof the feed pump 51, and is connected to the fuel tank 4 via the inlet 7a and the outlet 7 b of the aspirator 7. The fuel circulation pipeopening/closing solenoid valve 712 opens and closes the inlet 7 a of theaspirator 7 of the fuel circulation pipe 53. The feed pipeopening/closing solenoid valve 711 opens and closes the communication ofthe feed pipe 5 on the same side as the injection pump 1 with respect tothe branch point between the feed pipe 5 and the fuel circulation pipe53. The suction port opening/closing solenoid valve 72 opens and closesthe purge pipe 19 between the suction port 7 c of the aspirator 7 andthe fuel gallery 11 as well as the overflow fuel pipe 81.

The DME fuel retrieving control section 10 detects the operating/stoppedstate of the diesel engine (the injection/non-injection state of the DMEfuel supply device 100), and executes opening/closing control (ON/OFFcontrol) on the feed pump 51, the feed pipe opening/closing solenoidvalve 711, the fuel circulation pipe opening/closing solenoid valve 712,and the suction port opening/closing solenoid valve 72 according to eachof the states. During the stop of the diesel engine, the DME fuelretrieving control section 10 executes control to retrieve the DME fuelremaining in the fuel gallery 11 and the overflow fuel pipe 81.

Furthermore, the “remaining fuel retrieving means” also has thevapor-phase pressure delivery pipe 73 and the vapor-phase pressuredelivery pipe opening/closing solenoid valve 74 for opening and closingthe communication of the vapor-phase pressure delivery pipe 73, as meansfor connecting the outlet for the vapor phase 4 b in the fuel tank 4(the vapor-phase delivery port 43) and the inlet side of the fuelgallery 11 of the injection pump 1. The vapor-phase pressure deliverypipe 73 has the throttling section 75 whose inside diameter is partiallyreduced, and the vapor-phase pressure delivery pipe opening/closingsolenoid valve 74 is disposed at a position higher than the fuel gallery11 of the injection pump 1. The vapor-phase pressure delivery pipeopening/closing solenoid valve 74 is ON/OFF controlled by the DME fuelretrieving control section 10 so that the communication of thevapor-phase pressure delivery pipe 73 is opened when the vapor-phasepressure delivery pipe opening/closing solenoid valve 74 is in the ONcontrol state.

The DME fuel supply device 100 further has the low-pressure tank 17having a hermetically sealed structure smaller in capacity than the fueltank 4. The low-pressure tank 17 is constructed so that its internalpressure is brought to a low-pressure state when the low-pressure tank17 is sucked by the compressor 16, and so that the low-pressure state ismaintained by the check valve 171 even when the compressor 16 stops. Thelow-pressure tank 17 communicates with the overflow fuel pipe 81upstream of the overflow valve 82 through the purge pipe 19, and thepurge pipe 19 is provided with the purge pipe opening/closing solenoidvalve 18 capable of opening and closing the purge pipe 19. The purgepipe opening/closing solenoid valve 18 is controlled by the DME fuelretrieving control section 10, and during the stop of the diesel engine,the purge pipe opening/closing solenoid valve 18 is turned on andbrought to its open state so that the low-pressure tank 17 and theoverflow fuel pipe 81 communicate with each other, while during theoperation of the diesel engine, the purge pipe opening/closing solenoidvalve 18 is turned off and brought to its closed state so that thecommunication between the low-pressure tank 17 and the overflow fuelpipe 81 is cut off.

Next, the states of control of each of the feed pump 51, feed pipeopening/closing solenoid valve 711, the fuel circulation pipeopening/closing solenoid valve 712, and the suction port opening/closingsolenoid valve 72 by the DME fuel retrieving control section 10 in theDME fuel supply device 100 during stop, fuel charging, engine operationand retrieving of remaining fuel will be described with reference to thecorresponding drawings.

FIG. 10 is a schematic diagram showing the stopped state of the DME fuelsupply device 100 according to the invention of the present application.

During stop, the DME fuel retrieving control section 10 executes OFFcontrol on all of the feed pump 51, the feed pipe opening/closingsolenoid valve 711, the fuel circulation pipe opening/closing solenoidvalve 712, the suction port opening/closing solenoid valve 72, thevapor-phase pressure delivery pipe opening/closing solenoid valve 74,and the purge pipe opening/closing solenoid valve 18. During the OFFcontrol, the feed pump 51 is stopped, and all of the feed pipeopening/closing solenoid valve 711, the fuel circulation pipeopening/closing solenoid valve 712, the suction port opening/closingsolenoid valve 72, the vapor-phase pressure delivery pipeopening/closing solenoid valve 74 and the purge pipe opening/closingsolenoid valve 18 are closed. The feed pipe 5 is charged with DME fuelfrom the DME fuel delivery port 41 of the fuel tank 4 to the check valve713, and further, a section (reference numeral 5 a) between the checkvalve 713 and the closed feed pipe opening/closing solenoid valve 711 isheld in the state of being charged with DME fuel.

FIG. 11 is a schematic diagram showing the state of the DME fuel supplydevice 100 according to the invention of the present application duringfuel charging as well as during operation.

During the fuel charging of charging DME fuel into the injection systemsuch as the fuel gallery 11 from the stopped state, the DME fuelretrieving control section 10 executes ON control on the feed pipeopening/closing solenoid valve 711, and then executes ON control on thefeed pump 51. When the feed pipe opening/closing solenoid valve 711 isON controlled, the communication passage of the feed pipe 5 from thefeed pump 51 to the injection pump 1 is formed, and the DME fuel of thefuel tank 4 is delivered under pressure to the fuel gallery 11 by thefeed pump 51 (symbol A). As described above, the feed pipe 5 is held inthe state of being already charged with DME fuel during stop from theDME fuel delivery port 41 of the fuel tank 4 to the feed pipeopening/closing solenoid valve 711, so that when the DME fuel of thefuel tank 4 starts to be charged into the injection system such as thefuel gallery 11 during stop, the DME fuel immediately starts to becharged into the fuel gallery 11 of the injection pump 1. Accordingly,it is possible to reduce time taken to charge the DME fuel into theinjection system during fuel charging.

When the DME fuel is charged into the fuel gallery 11, the injectionpipe 3 and the overflow fuel pipe 81 (symbol B), the diesel engine isbrought to the operable state. When the diesel engine in this state isstarted and reaches the operating state, the cam in the cam chamber 12of the injection pump 1 rotates in conjunction with the operation of thediesel engine, thereby operating the compressor 16. As described above,DME fuel which has entered the cam chamber 12 is separated by the oilseparator 13 and is then returned to the fuel tank 4 by being sucked bythe compressor 16 (symbol C). The inside of the low-pressure tank 17 isalso sucked by the compressor 16 and maintained in the low-pressurestate.

FIG. 12 is a schematic diagram showing the state of the DME fuel supplydevice 100 according to the invention of the present application duringthe retrieving of remaining fuel, and shows the state in which DME fuelis being retrieved by the aspirator 7 (vapor-phase substitution).

After the diesel engine has been stopped, in order to retrieve to thefuel tank 4 the DME fuel remaining in the fuel gallery 11, the injectionpipe 3 and the overflow fuel pipe 81, the DME fuel retrieving controlsection 10 executes OFF control on the feed pipe opening/closingsolenoid valve 711 to cut off the communication passage of the feed pipe5 on the same side as the injection pump 1 with respect to the branchpoint between he feed pipe 5 and the fuel circulation pipe 53, therebycutting off the supply of DME fuel to the fuel gallery 11. When the DMEfuel retrieving control section 10 executes ON control to open the fuelcirculation pipe opening/closing solenoid valve 712, the DME fueldelivered from the feed pump 51 is delivered not to the injection pump 1but to the fuel circulation pipe 53, and is circulated from the fuelcirculation pipe 53 to the fuel tank 4 via the aspirator 7 (symbol D).

A ring-shaped flow of DME fuel including the aspirator 7 is formed, andsuction force is produced in the suction port 7 c of the aspirator 7.During this state, when the suction port opening/closing solenoid valve72 is controlled to open to provide communication between the suctionport 7 c of the aspirator 7 and the fuel gallery 11, the injection pipe3 as well as the overflow fuel pipe 81, the DME fuel remaining in thefuel gallery 11, the injection pipe 3 and the overflow fuel pipe 81 canbe sucked from the suction port 7 c of the aspirator 7. The DME fuelsucked from the suction port 7 c of the aspirator 7 is vaporized, i.e.,substituted by a vapor phase, and sucked from the suction port 7 c, bythe suction force produced in the suction port 7 c, and is retrieved tothe fuel tank 4 together with DME fuel which flows from the inlet 7 a tothe outlet 7 b of the aspirator 7 (symbol E).

In this manner, the fuel circulation pipe 53 is branched from the feedpipe 5 in the vicinity of the discharging port of the feed pump 51, andis connected to the fuel tank 4 via the inlet 7 a and the outlet 7 b ofthe aspirator 7, whereby the length of the circulation passage of DMEfuel including the aspirator 7 can be made short, and the flow passageresistance of the circulation passage can be made small. Accordingly, adecrease due to the flow passage resistance in the flow rate of DME fuelflowing in the circulation passage can be reduced, and a decrease in thesuction force produced in the suction port 7 c of the aspirator 7 can bereduced, whereby it is possible to improve the efficiency of retrievingof remaining fuel by the aspirator 7.

In addition, the fuel circulation pipe opening/closing solenoid valve712 and the feed pipe opening/closing solenoid valve 711 are constructedto be independently openable and closable, whereby after the DME fuelremaining in the fuel gallery 11, the injection pipe 3 and the overflowfuel pipe 81 has been retrieved by the aspirator 7, if the fuelcirculation pipe opening/closing solenoid valve 712 is closed with thefeed pipe opening/closing solenoid valve 711 remaining closed and thefeed pump 51 is stopped and the DME fuel supply device 100 is stopped,DME fuel can be held in the state of being charged between the feed pipeopening/closing solenoid valve 711 and the check valve 713. Accordingly,it is possible to reduce the amount of DME fuel to be retrieved by the“remaining fuel retrieving means”, and it is possible to reduce timetaken to retrieve DME fuel through the “remaining fuel retrievingmeans”.

Furthermore, it is more preferable to dispose the aspirator 7 and thefuel circulation pipe opening/closing solenoid valve 712 immediatelyclose to the fuel tank 4 so as to make the length of the fuelcirculation pipe 53 as short as possible. In this construction, sincethe flow passage resistance of the fuel circulation pipe 53 can beminimized, the efficiency of retrieving of remaining fuel by theaspirator 7 can be improved to a further extent.

Furthermore, it is more preferable that the feed pipe opening/closingsolenoid valve 711 be disposed as close as possible to the inlet of thefuel gallery 11 of the injection pump 1, and the check valve 713 bedisposed as immediately close as possible to the branch point betweenthe feed pipe 5 and the fuel circulation pipe 53. In this construction,since the amount of DME fuel to be held in the feed pipe 5 when the feedpipe opening/closing solenoid valve 711 is closed can be made farlarger, it is possible to further reduce time taken to charge DME fuelinto the injection system at the starting time of the diesel engine. Inaddition, since the amount of DME fuel remaining in the injectionsystem, which is to be retrieved after the stop of the diesel engine,can be made far smaller, it is possible to further reduce time taken toretrieve DME fuel remaining in the injection system after the stop ofthe diesel engine.

At the same time that the DME fuel of the fuel gallery 11 and theoverflow fuel pipe 81 is retrieved to the fuel tank 4 by being sucked bythe aspirator, the DME fuel retrieving control section 10 also executesON control to open the vapor-phase pressure delivery pipeopening/closing solenoid valve 74 and brings the vapor-phase pressuredelivery pipe 73 which connects the vapor phase 4 b of the fuel tank 4and the inlet of the fuel gallery 11, into a communicating state. TheDME fuel in a liquid state remaining in the fuel gallery 11 and theoverflow fuel pipe 81 is delivered under pressure to the suction port 7c of the aspirator 7 by the high pressure of the vapor phase 4 b (symbolF). In addition, this pressure is compressed to a far higher pressure bythe throttling section 75 where the inside diameter of the vapor-phasepressure delivery pipe 73 is partially reduced, whereby the remainingDME fuel can be delivered under pressure by a far higher pressure.

Accordingly, since the DME fuel in a liquid state is delivered underpressure to the suction port 7 c of the aspirator 7 by using thepressure of the vapor phase 4 b, it is possible to reduce time taken toretrieve the DME fuel remaining in the fuel gallery 11 and the overflowfuel pipe 81. The DME fuel retrieving control section 10, after thelapse of a predetermined time, closes only the vapor-phase pressuredelivery pipe opening/closing solenoid valve 74 and cuts off thecommunication with the vapor phase 4 b in a high-pressure state.Accordingly, since the inside of the fuel gallery 11 and that of theoverflow fuel pipe 81 can be brought into lower-pressure states, thevaporization of the DME fuel in a liquid state which remains withoutbeing delivered under pressure by vapor phase pressure can beaccelerated, whereby it is possible to further reduce time taken toretrieve the remaining DME fuel by the “remaining fuel retrievingmeans”.

In addition, in the DME fuel supply device 100, since the aspirator 7 isdisposed at a position lower than the fuel gallery 11, the injectionpipe 3 and the overflow fuel pipe 81, the DME fuel remaining in the fuelgallery 11, the injection pipe 3 and the overflow fuel pipe 81 isretrieved to the fuel tank 4 by a combined force of gravity and thesuction force produced in the suction port 7 c of the aspirator 7.Accordingly, it is possible to more efficiently retrieve the DME fuelremaining in the injection system by using gravity, and it is possibleto further reduce time taken to retrieve the DME fuel in the injectionsystem to the fuel tank 4 after the stop of the diesel engine.

In addition, since the vapor-phase pressure delivery pipeopening/closing solenoid valve 74 is disposed at a position higher thanthe fuel gallery 11, the DME fuel in a liquid state remaining in thefuel gallery 11, the injection pipe 3 and the overflow fuel pipe 81 isforcedly delivered under pressure to the suction port 7 c of theaspirator 7 by a combined force of gravity and the pressure of the vaporphase 4 b in the fuel tank 4. Accordingly, gravity can be used to moreefficiently deliver under pressure the DME fuel in a liquid stateremaining in the fuel gallery 11, the injection pipe 3 and the overflowfuel pipe 81 to the suction port 7 c of the aspirator 7, whereby it ispossible to further reduce time taken to retrieve the DME fuel remainingin the fuel gallery 11, the injection pipe 3 and the overflow fuel pipe81 to the fuel tank 4.

FIG. 13 is a schematic diagram showing the state of the DME fuel supplydevice 100 according to the invention of the present application duringthe retrieving of remaining fuel, and shows the state in which DME fuelis being sucked into the low-pressure tank 17.

After the DME fuel retrieving control section 10 has retrieved the DMEfuel remaining in the fuel gallery 11, the injection pipe 3 and theoverflow fuel pipe 81, by means of the aspirator 7 for a predeterminedtime, the DME fuel retrieving control section 10 executes OFF control tostop the feed pump 51, and executes OFF control on the vapor-phasepressure delivery pipe opening/closing solenoid valve 74 to cut off thecommunication between the vapor phase 4 b of the fuel tank 4 and theinlet of the fuel gallery 11. Then, the DME fuel retrieving controlsection 10 executes OFF control on the fuel circulation pipeopening/closing solenoid valve 712 to cut off the circulation passage ofthe fuel circulation pipe 53, and executes OFF control to close thesuction port opening/closing solenoid valve 72 and cut off thecommunication between the overflow fuel pipe 81 and the suction port 7 cof the aspirator 7. Then, the DME fuel retrieving control section 10executes ON control to open the purge pipe opening/closing solenoidvalve 18 and provide communication between the low-pressure tank 17maintained in an approximately constant low pressure state and the purgepipe 19. The residual DME fuel remaining in the fuel gallery 11, theinjection pipe 3 and the overflow fuel pipe 81 is sucked into thelow-pressure tank 17 by the negative pressure in the low-pressure tank17 via the purge pipe 19 (symbol G). When the diesel engine again startsand the compressor 16 is activated, the DME fuel sucked into thelow-pressure tank 17 is sucked by the compressor 16 and is retrieved tothe fuel tank 4 (symbol H).

Accordingly, since the purge pipe opening/closing solenoid valve 18 isturned on after the DME fuel remaining in the fuel gallery 11 and theoverflow fuel pipe 81 has been retrieved to some extent by the aspirator7, the DME fuel remaining without being completely retrieved by theaspirator 7 can be rapidly sucked and retrieved into the low-pressuretank 17. Accordingly, it is possible to further reduce time taken toretrieve DME fuel by the “remaining fuel retrieving means”.

In this manner, it is possible to reduce time taken to retrieve the DMEfuel in the injection system to the fuel tank 4 after the stop of thediesel engine. It is also possible to reduce time taken to charge DMEfuel into the injection system from the fuel tank 4 at the starting timeof the diesel engine.

As another embodiment, there is provided the DME fuel supply device 100for a common rail diesel engine in which a common rail is providedbetween the injection pump 1 and the injection nozzle 9 in theabove-mentioned fourth embodiment.

FIG. 14 is a schematic diagram showing a sixth embodiment of the DMEfuel supply device 100 according to the invention of the presentapplication, and shows the DME fuel supply device 100 for a common raildiesel engine in which the vapor-phase pressure delivery pipe 73 isconnected to a common rail. FIG. 15 is a schematic diagram showing aseventh embodiment of the DME fuel supply device 100 according to theinvention of the present application, and shows the DME fuel supplydevice 100 for a common rail diesel engine in which the vapor-phasepressure delivery pipe 73 is connected to the injection pipe 3.

In the above-mentioned fifth embodiment, the injection nozzle 9 isconstructed to be opened for injection of DME fuel by the pressure ofDME fuel delivered under pressure from the injection pump 1 to theinjection pipe 3. For this reason, when the injection pipe 3 isconnected to the vapor-phase pressure delivery pipe 73, there is apossibility that the pressure in the injection pipe 3 becomes unstable,and there is a risk that the fuel injection characteristics of theinjection nozzle 9 become unstable. Therefore, the vapor-phase pressuredelivery pipe 73 cannot be connected to the injection pipe 3.

On the other hand, the DME fuel supply device 100 for a common raildiesel engine has a construction in which DME fuel is delivered underpressure from the injection pump 1 to the common rail 91 and the DMEfuel in the common rail 91 maintained in a given high-pressure state isdelivered to each injection nozzle 9. For this reason, the common raildiesel engine adopts the injection nozzle 9 having an electromagnetictype of valve opening mechanism. This injection nozzle 9 is not easilyinfluenced by pressure variations in the injection pipe 3.

Accordingly, in the DME fuel supply device 100 for a common rail dieselengine, as shown in FIG. 6, the vapor-phase pressure delivery pipe 73can be connected to the common rail 91 (embodiment 6). Accordingly,while the DME fuel remaining in the common rail 91, the fuel gallery 11and the overflow fuel pipe 81 is being retrieved to the fuel tank 4 bythe above-mentioned “remaining fuel retrieving means”, the DME fuel in aliquid state remaining in the common rail 91 can be forcedly deliveredunder pressure to the aspirator 7 by the pressure of the vapor phase 4 bin the fuel tank 4. Accordingly, it is possible to further reduce timetaken to retrieve the DME fuel remaining in the common rail 91 to thefuel tank 4 by means of the aspirator 7. In addition, since thevapor-phase pressure delivery pipe opening/closing solenoid valve 74which opens and closes the vapor-phase pressure delivery pipe 73 isdisposed at a position higher than the common rail 91, the DME fuel in aliquid state remaining in the common rail 91 can be more efficientlyforcedly delivered under pressure to the aspirator 7 by a combined forceof gravity and vapor phase pressure. As to the sixth embodiment (FIG.14) and the seventh embodiment (FIG. 15), the description of sectionswhich have the same constructions as the corresponding ones of the firstembodiment is omitted herein.

Furthermore, in the DME fuel supply device 100 for a common rail dieselengine, as shown in FIG. 15, the vapor-phase pressure delivery pipe 73may also be connected to the vicinity of the injection nozzle 9 of theinjection pipe 3 (the inlet side of the injection nozzle 9) (embodiment7). If the vapor-phase pressure delivery pipe 73 is connected in thismanner to the vicinity of the injection nozzle 9 of the injection pipe 3disposed at a position far higher than the common rail 91, not only theDME fuel remaining in the common rail 91 but also the DME fuel remainingin the injection pipe 3 can be delivered under pressure directly to theaspirator 7 by vapor phase pressure. Accordingly, it is possible tofurther reduce time taken to retrieve the DME fuel remaining in thecommon rail 91 and the injection pipe 3 to the fuel tank 4 by means ofthe aspirator 7. In addition, since the vapor-phase pressure deliverypipe opening/closing solenoid valve 74 which opens and closes thevapor-phase pressure delivery pipe 73 is disposed at a position higherthan the injection pipe 3, the DME fuel in a liquid state remaining inthe injection pipe 3 can be more efficiently forcedly delivered underpressure to the aspirator 7 by a combined force of gravity and vaporphase pressure.

It goes without saying that the invention is not limited to any of theabove-mentioned embodiments, and various modifications can be madewithout departing from the scope of the invention described in theappended claims and are included in the scope of the invention.

According to the invention, in a liquefied gas fuel supply device for adiesel engine, it is possible to reduce time taken to retrieve liquefiedgas fuel in an injection system to a fuel tank after the stop of thediesel engine.

In addition, in the liquefied gas fuel supply device for the dieselengine, it is possible to reduce time taken to charge liquefied gas fuelin the injection system to the fuel tank at the starting time of thediesel engine.

INDUSTRIAL APPLICABILITY

The invention can be applied to liquefied gas supply devices for dieselengines which use liquefied gases such as DME or high cetane number LPgases as their fuels.

1. A liquefied gas fuel supply device for a diesel engine characterizedby comprising: a fuel tank for reserving liquefied gas fuel; aninjection pump for delivering liquefied gas fuel to a fuel injectionnozzle of a diesel engine; fuel supply means for delivering theliquefied gas fuel from the fuel tank to the injection pump; andremaining fuel retrieving means for retrieving liquefied gas fuelremaining in the injection pump to the fuel tank, after the stop of thediesel engine, the remaining fuel retrieving means being constructed tocause forced circulation of the liquefied gas fuel in the fuel tank backso as to again return the liquefied gas fuel to the fuel tank through anaspirator, and retrieve the liquefied gas fuel remaining in theinjection pump to the fuel tank by suction force produced in a suctionport of the aspirator by the forced circulation, the suction port of theaspirator being disposed at a position lower than an area in theinjection pump in which the liquefied gas fuel remains.
 2. A liquefiedgas fuel supply device for a diesel engine characterized by comprising:a feed pump for pressurizing liquefied gas fuel in a fuel tank to apredetermined pressure and delivering the liquefied gas fuel to a feedpipe; an injection pump for delivering the liquefied gas fuel in a fuelgallery into which the liquefied gas fuel delivered via the feed pipeflows, to an injection nozzle of a diesel engine by a predeterminedamount at predetermined timing; an overflow fuel pipe for returning tothe fuel tank the liquefied gas fuel which overflows from the injectionpump; and remaining fuel retrieving means for retrieving to the fueltank the liquefied gas fuel remaining in the fuel gallery and theoverflow fuel pipe, after the stop of the diesel engine, the remainingfuel retrieving means having: a fuel circulation pipe branched from thefeed pipe at an intermediate point thereof and connected to the fueltank; feed pipe opening/closing means provided in the feed pipe on aside downstream of the feed pump in a flowing direction of the liquefiedgas fuel, and operative to open and close a flow passage of the feedpipe; and an aspirator provided in the fuel circulation pipe and havinga suction port disposed to communicate with the fuel gallery and/or theoverflow fuel pipe, the remaining fuel retrieving means beingconstructed to circulate the liquefied gas fuel delivered from the feedpump, to the fuel tank via the feed pipe, the fuel circulation pipe andthe aspirator in the state of cutting off supply to the injection pumpby closing the feed pipe opening/closing means, and suck and retrievethe liquefied gas fuel remaining in the fuel gallery and the overflowfuel pipe, to the fuel tank by suction force produced in the suctionport of the aspirator on the basis of the circulation, the suction portof the aspirator being disposed at a position lower than the fuelgallery and the overflow fuel pipe.
 3. A liquefied gas fuel supplydevice for a diesel engine according to claim 2, characterized byfurther comprising a check valve disposed between a position where thefuel circulation pipe is branched from the feed pipe and the feed pipeopening/closing means, and operative to prevent liquefied gas fuel fromflowing back from the injection pump, and fuel circulation pipeopening/closing means provided in the fuel circulation pipe andoperative to open and close a flow passage of the fuel circulation pipe.4. A liquefied gas fuel supply device for a diesel engine characterizedby comprising: a feed pump for pressurizing liquefied gas fuel in a fueltank to a predetermined pressure and delivering the liquefied gas fuelto a feed pipe; an injection pump for delivering the liquefied gas fuelin a fuel gallery into which the liquefied gas fuel delivered via thefeed pipe flows, to an injection nozzle of a diesel engine by apredetermined amount at predetermined timing; an overflow fuel pipe forreturning to the fuel tank the liquefied gas fuel which overflows fromthe injection pump; and remaining fuel retrieving means for retrievingto the fuel tank the liquefied gas fuel remaining in the fuel galleryand the overflow fuel pipe, after the stop of the diesel engine, theremaining fuel retrieving means having; a fuel circulation pipe branchedfrom the feed pipe at an intermediate point thereof and connected to thefuel tank; feed pipe opening/closing means provided in the feed pipe ona side downstream of the feed pump in a flowing direction of theliquefied gas fuel, and operative to open and close a flow passage ofthe feed pipe; and an aspirator provided in the fuel circulation pipeand having a suction port disposed to communicate with the fuel galleryand/or the overflow fuel pipe, the remaining fuel retrieving means beingconstructed to circulate the liquefied gas fuel delivered from the feedpump, to the fuel tank via the feed pipe, the fuel circulation pipe andthe aspirator in the state of cutting off supply to the injection pumpby closing the feed pipe opening/closing means, and suck and retrievethe liquefied gas fuel remaining in the fuel gallery and the overflowfuel pipe, to the fuel tank by suction force produced in the suctionport of the aspirator on the basis of the circulation, the remainingfuel retrieving means further including: fuel circulation pipeopening/closing means provided in the fuel circulation pipe andoperative to open and close a flow passage of the fuel circulation pipe;and a check valve disposed between a branch point between the feed pipeand the fuel circulation pipe and the feed pipe opening/closing means,and operative to prevent liquefied gas fuel from flowing back from theinjection pump.
 5. A liquefied gas fuel supply device for a dieselengine according to any one of claims 1 to 4, characterized by furthercomprising a vapor-phase pressure delivery pipe connecting an inlet forliquefied gas fuel in the injection pump and a vapor phase in the fueltank, and vapor-phase pressure delivery pipe opening/closing means foropening and closing the vapor-phase pressure delivery pipe.
 6. Aliquefied gas fuel supply device for a diesel engine according to claim5, characterized in that the vapor-phase pressure delivery pipeopening/closing means is disposed at a position higher than an area inthe injection pump in which the liquefied gas fuel remains.
 7. Aliquefied gas fuel supply device for a diesel engine according to anyone of claims 1 or 2, characterized by including a construction in whichthe liquefied gas fuel delivered from the injection pump is supplied toa common rail and is delivered to each fuel injection nozzle from thecommon rail, and further comprising a vapor-phase pressure delivery pipeconnecting the common rail and a vapor phase in the fuel tank, andvapor-phase pressure delivery pipe opening/closing means for opening andclosing the vapor-phase pressure delivery pipe.
 8. A liquefied gas fuelsupply device for a diesel engine according to claim 7, characterized inthat the vapor-phase delivery pipe opening/closing means is disposed ata position higher than the common rail.
 9. A liquefied gas fuel supplydevice for a diesel engine according to any one of claims 1 or 2,characterized by including a construction in which the liquefied gasfuel delivered from the injection pump is supplied to a common rail andis delivered to each fuel injection nozzle from the common rail, andfurther comprising a vapor-phase pressure delivery pipe connecting aninlet of the fuel injection nozzle and a vapor phase in the fuel tank,and vapor-phase pressure delivery pipe opening/closing means for openingand closing the vapor-phase pressure delivery pipe.
 10. A liquefied gasfuel supply device for a diesel engine according to claim 9,characterized in that the vapor-phase pressure delivery pipeopening/closing means is disposed at a position higher than the fuelinjection nozzle.
 11. A liquefied gas fuel supply device for a dieselengine according to claim 2, characterized by further comprising: an oilseparator for separating the liquefied gas fuel mixing with alubricating oil in a cam chamber of the injection pump which is adedicated lubricating system separated from a lubricating system for adiesel engine; a compressor for pressurizing the liquefied gas fuelseparated by the oil separator and delivering the liquefied gas fuel tothe fuel tank; a low-pressure tank connected to a suction port of thecompressor; a purge pipe causing the low-pressure tank and the overflowfuel pipe to communicate with each other; and purge pipe opening/closingmeans capable of opening and closing the purge pipe.
 12. A liquefied gasfuel supply device for a diesel engine according to claim 11characterized in that a check valve for holding pressure in thelow-pressure tank is disposed between the compressor and thelow-pressure tank.
 13. A liquefied gas fuel supply device for a dieselengine according to claim 11, characterized in that the remaining fuelretrieving means includes: the feed pipe opening/closing means and thefuel circulation pipe opening/closing means for switching a deliveryport of the feed pipe to either one of an inlet of a circulation passageof the aspirator and an inlet of the fuel gallery and causing thedelivery port to communicate with the either one; suction portopening/closing means for opening and closing communication between thesuction port of the aspirator and the fuel gallery as well as theoverflow fuel pipe; and a liquefied gas fuel retrieving control sectioncapable of executing control to switch communication provided by each ofthe feed pipe opening/closing means and the fuel circulation pipeopening/closing means to the inlet of the aspirator, open the suctionport opening/closing means, and form a flow passage through which theliquefied gas fuel delivered from the feed pump is to be circulated tothe fuel tank, as well as control to open the vapor-phase pressuredelivery pipe opening/closing means and, after the lapse of apredetermined time, close only the vapor-phase pressure delivery pipeopening/closing means.
 14. A liquefied gas fuel supply device for adiesel engine according to claim 13, characterized in that the liquefiedgas fuel retrieving control section is constructed to be able to executecontrol to open the purge pipe opening/closing means after closing thesuction port opening/closing means.
 15. A liquefied gas fuel supplydevice for a diesel engine according to claim 11, characterized in thatthe liquefied gas fuel retrieving control section is constructed to beable to execute, after the stop of a diesel engine, control to close thefeed pipe opening/closing means and cut off supply of liquefied gas fuelto the fuel gallery, and execute, after stopping the feed pump with thesuction port opening/closing means closed, control to open the purgepipe opening/closing means and suck the liquefied gas fuel remaining inthe fuel gallery and the overflow fuel pipe to the low-pressure tank.16. A liquefied gas fuel supply device for a diesel engine according toclaim 3, characterized in that the remaining fuel retrieving meansincludes feed pipe opening/closing means for opening and closingcommunication of the feed pipe on the same side as the injection pumpwith respect to the branch point between the feed pipe and the fuelcirculation pipe; fuel circulation pipe opening/closing-means foropening and closing an inlet of the aspirator; suction portopening/closing means for opening and closing a communication pipebetween the suction port of the aspirator and the fuel gallery as wellas the overflow fuel pipe; and a liquefied gas fuel retrieving controlsection for executing control to open and close the feed pump, the feedpipe opening/closing means, the fuel circulation pipe opening/closingmeans, and the suction port opening/closing means, the liquefied gasfuel retrieving control section being constructed to be able to execute,after the stop of a diesel engine, control to close the feed pipeopening/closing means and cut off supply of liquefied gas fuel to thefuel gallery, and control to circulate the liquefied gas fuel deliveredfrom the feed pump to the fuel tank via the fuel circulation pipe whilecausing the suction port of the aspirator to communicate with the fuelgallery as well as the overflow fuel pipe, by executing control to openthe fuel circulation pipe opening/closing means and the suction portopening/closing means.
 17. A liquefied gas fuel supply device for adiesel engine according to claim 16, characterized in that the liquefiedgas fuel retrieving control section is constructed to be able to executecontrol to hold the liquefied gas fuel in the state of being charged inthe feed pipe between the feed pipe opening/closing means and the checkvalve, while continuing control to close the feed pipe opening/closingmeans, after having retrieving to the fuel tank the liquefied gas fuelremaining in the fuel gallery and the overflow fuel pipe.
 18. Aliquefied gas fuel supply device for a diesel engine according to claim16, characterized in that in the remaining fuel retrieving means, theaspirator and the fuel circulation pipe opening/closing means aredisposed immediately close to the fuel tank.
 19. A liquefied gas fuelsupply device for a diesel engine according to claim 16, characterizedin that in the remaining fuel retrieving means, the feed pipeopening/closing means is disposed in the feed pipe in the vicinity of aninlet of the fuel gallery, and the check valve is disposed immediatelyclose to the branch point between the feed pipe and the fuel circulationpipe.
 20. A liquefied gas fuel supply device for a diesel engineaccording to claim 16, characterized in that the liquefied gas fuelretrieving control section is constructed to be able to execute controlto open the vapor-phase pressure delivery pipe opening/closing means anddeliver vapor-phase pressure in the fuel tank to the fuel gallery andthe overflow fuel pipe.